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Comment by boulos | Hacker News Reader

I appreciate that you didn't sling mud at Azure, but re-reading the commit for the move to Azure [1] there were tell tale signs then that it might be bumpy for the storage layer.

For what it's worth, hardware doesn't provide an IOPS/latency SLA either ;). In all seriousness, we (Google, all providers) struggle with deciding what we can strictly promise. Offering you a "guaranteed you can hit 50k IOPS" SLA isn't much comfort if we know that all it takes is a single ToR failure for that to be not true (providers could still offer it, have you ask for a refund if affected, etc. but your experience isn't changed).

All that said, I would encourage you to reconsider. I know you're frustrated, but rolling your own infrastructure just means you have to build systems even better than the providers. On the plus side, when it's your fault, it's your fault (or the hardware vendor, or the colo facility). You've been through a lot already, but I'd suggest you'd be better off returning to AWS or coming to us (Google) [Note: Our PD offering historically allowed up to 10 TiB per disk and is now a full 64 TiB, I'm sorry if the docs were confusing].

Again, I'm not saying this to have you come to us or another cloud provider, but because I honestly believe this would be a huge time sink for GitLab. Instead of focusing on your great product, you'd have to play "Let's order more storage" (honestly managing Ceph has a similar annoyance). I'm sorry you had a bad experience with your provider, but it's not all the same. Feel free to reach out to me or others, if you want to chat further.

Disclosure: I work on Google Cloud.

[1] https://gitlab.com/gitlab-com/www-gitlab-com/merge_requests/...

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> rolling your own infrastructure just means you have to build systems even better than the providers

As a cloud provider, though, you're trying to provide shared resources to a group of clients. A company rolling their own system doesn't have to share, and they can optimise specifically for their own requirements. You don't get these luxuries, and it's reasonable to expect a customised system to perform better than a general one.

As a counter argument: very few teams at Google run on dedicated machines. Those that do are enormous, both in the scale of their infrastructure and in their team sizes. I'm not saying always go with a cloud provider, I'm reiterating that you'd better be certain you need to.

But some workloads get all the priority while others get zero/idle priority. Not true in public cloud.

Using a resource abstraction layer such as mesos can alleviate this downside by consolidating many of your workloads onto a pool of large dedicated machines.

Multitenancy is a large part of what makes public cloud providers profitable, but they all understand the need to isolate customer resources as much as possible.

Interesting, presumably they're very well informed and they obviously feel that Google's cloud offerings are the best way to go.

If I may ask a few questions:

- Are they charged the same as external customers or do they get a 'wholesale' rate?

- As internal clients, do they run under the same conditions as external clients? Or is there a shared internal server pool that they use?

- Do they get any say in the hardware or low-level configuration of the systems they use? (ie. if someone needs ultra low latency or more storage, can they just ask Joe down the hall for a machine on a more lightly loaded network, or with bunch more RAM, for the week?)

- Do they have the same type of performance constraints as the ones encountered by gitlab?

I feel like most of the reason to use cloud services is when you have little idea what your actual requirements are, and need the ability to scale fast in both directions. Once you're established and have a fairly predictable workload, it makes more sense to move your hosting in-house.

The Google teams that he's referring to probably don't run on Google Cloud Platform, and rather run on Google's internal infrastructure that GCP is built upon. So most of your questions may not apply. However, his points about cloud infrastructure are still valid.

If you're right, then Google teams using internal Google server infrastructure is literally Google rolling their own.

He technically only said they don't run on dedicated machines, not that they run on GCP. My guess would be Google has some sort of internal system that probably uses a bunch of the same software but is technically not GCP.

This is mostly speculation base don having read this http://shop.oreilly.com/product/0636920041528.do

Hopefully someone who actually knows what theyre talking about will be along shortly!

> Are they charged the same as external customers or do they get a 'wholesale' rate?

Id be quite surprised if internal customers are charged a markup. Presumably the whole point in operating an internal service is that you lower the cost as much as possible for your internal customers.

> As internal clients, do they run under the same conditions as external clients? Or is there a shared internal server pool that they use?

From the above book, it seems that the hardware is largely abstracted away so most services aren't really aware of servers. I assume there's some separation between internal and external customers, but at a guess that'd largely be because of the external facing services being forks of existing internal tools that have been untangled from other internal services.

> Do they get any say in the hardware or low-level configuration of the systems they use? (ie. if someone needs ultra low latency or more storage, can they just ask Joe down the hall for a machine on a more lightly loaded network, or with bunch more RAM, for the week?)

As above, the hardware is largely abstracted away. From memory, teams usually say "we think we need ~x hrs of cpu/day, y Gbps of network,..." then there's some very clever scheduling that goes on to fit all the services on to the available hardware. There's a really good chapter on this in the above book.

> Do they have the same type of performance constraints as the ones encountered by gitlab?

Presumably it depends entirely on the software being written.

In the end it doesn't really say that they rolled their own on prem solution. For the kind of money they were forking out in the cloud you could just buy a Netapp or Isilon and get something that provides enough consistent storage performance. You don't need a distributed FS for the kinds of numbers they're looking at, using one is just a complicated way of working around the underlying limitations of cloud storage. In your own datacentre getting storage that works is pretty easy.

Most appliances are not geared towards many small random reads. And if you scale they start to be very expensive. And we would love to use an open source solution all our users can reuse.

I'm not an expert in Ceph but I've built many other storage solutions and typically where distributed filesystems fall down in performance is with small files. Even something like an Isilon can get into trouble with those kinds of workloads. The files are too small to be striped across multiple nodes and there's a lot of metadata overhead. Monolithic systems tend to do better with small files but even then you can run into trouble at the protocol (NFS) level with the metadata.

Disk systems do get expensive at scale but the scale that they're usually sold at these days is pretty huge. You talk about going up to a petabyte but that's a fraction of a single rack's worth of disk these days. Not everyone wants to be a filesystem expert and distributed filesystems are jumping in at the deep end.

You are right regarding many small files. Interestingly reading from many small files didn't seem to be so much of a problem with CephFS as it was to keep a large file open while reading and writing to it from thousands of processes (the legacy authorized_keys file).

Clearly CephFS as weak spots, but for what I've seen those are sports that we can work out, rough edges here and there. The good thing is that we are much more aware of these edges.

We are already working on what the next step will be to soften out these weaknesses so we are not impacted again. And of course to ship this to all our customers, either they run on CephFS, NFS appliances, local disks or whatever makes sense for them.

FYI. The kernel Ceph client has local fscache cache. I added it to the kernel :) https://lwn.net/Articles/563146/

We started using Ceph because we wanted to be able to grow our storage and compute independently. While it worked well for us we ended up having much larger latencies is as a result of this. So we developed FSCache support.

Even better yet, if you data is inherently shareable (or has some kind of locational affinity) you can end up always serving data with a Ceph backend from the local cache with the exception of a server going down or occasional request. I'm guessing it is (repo / account)

On your API machines serving out the git content of out the DFS you can setup a local SSD drive to read only caching. Depending on you workload you can end up significantly reducing the IOPs on the OSDs and also lowering network bandwidth.

With the network / IOPs savings we've decided to run our CephFS backed by Erasure Coded pool. Now we have lower cost of storage (1.7x vs 3x replication) and better reliability because now with our EC profile we can lose 5 chunks before data loss instead of 2 like before. That's because we more the 90% of requests are handled with local data and there's a long tail of old data that rarely accessed.

If you're going to give it a try, make sure you're using a recentish kernel such as a late 3.x series (or 4+). That has all the Cephfs FSCache / and upstream FSCache kinks work out. If you're using relatively recent kernel such late 3.x series or 4+ (as in ubuntu 16.04).

Thanks mtanski, this is great data.

We are running a recent kernel as in ubuntu 16.04.

The reason I'm framing the caching not so much at the CephFS level is because we are shipping a product, and I don't think that all our customers will be running CephFS on their infra. Therefore we will need to optimize for that use case also, and not only focus on what we do at GitLab.com.

Thanks for sharing! Will surely take a look at this.

I just want to note that the blog post you linked to was never actually published since we decided against pointing fingers when – by and large – the problems weren't their fault and their engineers were quite helpful. See the comment at the bottom of that thread[1] from Sid.

We made mistakes ourselves that were the root of the problems at the time, and based on the update[2] a few months later things definitely improved significantly.

[1]: https://gitlab.com/gitlab-com/www-gitlab-com/merge_requests/... [2]: https://gitlab.com/gitlab-com/www-gitlab-com/merge_requests/...

Sorry about that! I was on my phone, and followed the first thing from the linked post/issue; I didn't realize it wasn't published.

No problem, the thread is pretty long, and it's not necessarily easy to tell without understanding how our blog post process works. :)

Judging by the posts.

Random thought: Go talk to google and get $100k of free cloud credits.

You run 100 instances of n1-highcpu-2 (2 CPU, 2GB RAM), with a local 375 SSD. That gives you 37TB of storage and you're fine for the year.

This is an absolutely ridiculous setup but it could work.

1) Servers don't need to have more memory for caching. Local SSD access is fast enough.

2) Servers have 1Gb uplink. That can be saturated easily by a single local SSD.

3) I'm a firm believer that if you put 8-16 disks in a single box, you're gonna hit a hard limit with the network bandwidth and infrastructure (among other things).

4) Do you need IOPS or do you need storage???

5) Can CephFS shard fairly across a hundred systems?

6) Should CephFS run on raw disks, manage replica itself? and can it handle failure?

Bonus question) Why are we thinking about all of this. You should have just used s3?

> Bonus question) Why are we thinking about all of this. You should have just used s3?

NFS and Ceph both support the standard POSIX file access model, notably including random-access reads and writes on a file without replacing the entire file and consistency models that let you reason about directories and their contents usefully. If your goal is to run the reference implementation of git, or something that is compatible with it, on the filesystem, you absolutely need something that supports this.

You could write something new that speaks the git protocol but is designed to be backed by an eventually-consistent object store instead of a POSIX-compliant file store ... but that seems like an equally big challenge, honestly.

Fun aside. Google wrote a backend to Mercurial so it could be stored on bigtable. They did a talk about it 7 years ago.

http://m.youtube.com/watch?v=ri796Hx8las

And to SVN! https://lwn.net/Articles/194667/

It's not a bad decision; getting POSIX semantics to play well with modern expectations of a highly-consistent and highly-available distributed system is very difficult. But it's a work-intensive decision, and figuring out how to deploy NFS or Ceph at scale might be less work. Especially if Google's SVN/hg developers can work directly with the Bigtable developers on features, and GitLab's developers can't work directly with the S3 team (but can own their own Ceph or NFS stack).

Their Git hosting was also running on that same backend (I was on the team managing those products). But to a previous posters point That is a lot of work both to implement as well as to maintain. If you can just use a distributed filesystem you might save yourself some trouble.

Others have done this with libgit2 storage backends.

Anyone in particular, or anything open source? I could use this for a work project, but the closest I've been able to find is an old project which backed JGit to Cassandra and the Dulwich Swift backend[1].

[1]: https://www.dulwich.io/apidocs/dulwich.contrib.swift.html

We looked at this but it didn't have either the features or the speed we needed. I do think it is very promising.

Yes, write a Git backend using a distributed actor system, like Akka, Orleans or Service Fabric, backed by Table Storage, Bigtable or some other distributed hashtable store. Git maps naturally to this structure, using git hashes as table index.

You'll have a really cheap and very scalable solution that uses low level storage mechanisms yet it will also be really performant because when loaded everything will be served from memory.

For sure, and people are trying to do this on the basis of libgit2. But so far nobody has been able to make it work for all of the cases. Even GitHub is using filesystems as far as I know.

One of the teams I work closely with used JGit's extensibility to run git on top of a KVS: https://medium.com/@palantir/stemma-distributed-git-server-7...

Notably this doesn't require a distributed filesystem.

That looks really interesting, thanks for posting. I added it to our issue https://gitlab.com/gitlab-com/infrastructure/issues/727#note...

Relevant: http://githubengineering.com/introducing-dgit/

For Visual Studio Online and TFS, Microsoft is using libgit2 and some custom ASP.NET code for the upload-pack / receive-pack endpoints, stuffing the data into SQL Azure. No filesystem, no `git` executable.

We're currently at 70TB and we're planning for a 256TB setup https://docs.google.com/spreadsheets/d/1XG9VXdDxNd8ipgPlEr7N... . So that would be a lot of servers. I don't think SSDs for the file storage are affordable. We'll use SSDs for the journals.

I think that's a false assumption. Especially in 2016.

Unless something changed dramatically at GitHub they're a 100% solid-state fleet since 2012 when they started down the "building their datacenter cages" journey.

Whilst you could say as the 500lb gorilla in the market they can afford that luxury, there are other examples, i.e. DigitalOcean, where SSD is a core part of their product and it is offered inexpensively ($5/mo).

Even if you're looking at 3-way replication of your data, meaning you're buying 768TB of storage, the SSD should only tot up to $200-300k for Intel S3510 (or similar).

There's a non-trivial amount of additional effort involved in any kind of "multi-layered" storage (c.f. data on 7200rpm, NVMe cache) over and above just making all of your storage moderately performant in IOPS terms. That has cost too.

If you're rolling your own, you can tune these things.

For example, in this case, since they're IOPs-bound first, and probably network-bound second, you can cram 16 SSDs in a box, and then put a dual-port 25Gig Ethernet NIC up to 2 leaf switches at the top of rack, and then build a CLOS out of 100G spine switches, so that there are essentially never any network bottlenecks for Ceph.

This is very similar to DreamHost's DreamCompute cluster design, though they're using 2x 10G to the servers, and 40G up to the spines, since 25G/100G wasn't available when they built the cluster.

An alternative to user5994461's suggestion would be to switch from CephFS to a different distributed filesystem. If you need POSIX and can't go directly to S3 you could try ObjectiveFS[1]. Using local SSD instance store and memory for caching you can get very good performance even for small file workloads[2].

[1]: https://objectivefs.com [2]: https://objectivefs.com/howto/performance-amazon-efs-vs-obje...

ObjectiveFS looks interesting but I wonder about the latency if you do many small random reads (this is what we're seeing with git).

Latency for small random reads (16 parallel threads), using the Linux kernel source tree, when hitting in the SSD instance store disk cache have a 95th-percentile latency of 6ms with ~50MB/s throughput. When hitting in the memory cache the 95th-percentile latency is <1ms with ~380MB/s throughput. We have more performance data available at https://objectivefs.com/howto/performance-amazon-efs-vs-obje...

That sounds very good, but I think we prefer Ceph because it is better known. Do you have a comparison between Ceph and ObjectiveFS?

Another option would be to move to HDFS. HopsFS, a new distribution, can scale to over 1m ops/sec: http://www.logicalclocks.com/index.php/2016/10/14/hops-smash...

As someone who has run Hdfs in production on bare metal, I wonder how much you dislik gitlab...

TL;DR - HDFS is rarely the answer, mainly due to pains usually involving crashed nameservers.

HopsFS has multiple redundant, stateless NameNodes.

I think what you're seeing in this post has product implications for Google Cloud.

The OP is asking for guaranteed IOPS/latency SLA for which they're willing to pay HUGE money for by ROLLING THEIR OWN.

Possibly think about high service pricing tiers for systems that require it. This is a standard operations problem that can co-exist within pooled service models.

See my note about SLAs and ToR failures. We probably could promise something for our Local SSD offering (tail latency < 1ms!), but high-performance, guaranteed networked storage is just tricky.

As I said, rolling your own will not give you a guarantee, it will just give you the responsibility for failure. We don't offer the guarantee, because we don't want you to believe it can't fail.

At a certain scale, it's better to just take that responsibility rather than rely on someone to be able to handle that burden. When something fails, the worst thing is being out of control of it and unable to do anything about it.

Last time I had a failed storage controller, HP delivered a replacement in four hours. Last time a service provider went down, I had no visibility into the repair process, and had to explain there was nothing I could do... For five days.

It seems like you've outright admitted you can't guarantee what they need, yet you still urge them not to leave your business model. Maybe come back when your business model can meet their needs.

I think you're missing the point a bit -- the claim is not that the business model prevents these guarantees, but that it's inherently difficult for any party to do.

> had to explain there was nothing I could do... For five days

The good alternative would be that you controlled the infrastructure and it didn't break. The bad alternative is you directly control infrastructure, it breaks, and then you get fired.

Wikipedia, Stack Overflow, and Github all do just fine hosting their own physical infrastructure.

It's untrue that "the cloud" is always the right way. When you're on a multi-tenant system, you will never be the top priority. When you build your own, you are.

Google and AWS have vested interests (~30% margins) in getting you into the cloud. Always do the math to see if it's cost effective comparatively speaking.

That's not a strawman. It's just a false statement.

Thanks for the correction.

Sure and GitHub also has literally an order of magnitude more infrastructure than is being discussed in these proposals and retains Amazon Web Services and Direct Connect for a bunch of really good reasons.

Transparency from GitLab is excellent but you shouldn't really generalise statements about cloud suitability without the full picture or "Walking a mile in their shoes".

Yep, and we at GitLab have Direct Connect to AWS as a requirement for picking out new colo.

If you guys use AWS, have you taken a look at EBS provisioned IOPS? EBS provisioned IOPS comes to mind here since it allows you to specify the desired IOPS of a volume, and provides an SLA.

> Providers don't provide a minimum IOPS, so they can just drop you.

The reason I ask is because the blog post generalizes a lot about what cloud providers offer or what the cloud is capable of, but doesn't explore some of the options available to address those concerns, like provisioned IOPS with EBS, dedicated instances with EC2, provisioned throughput with DynamoDB, and so on.

EBS goes up to 16TB, we need an order of magnitude more.

You're right that the blog post was generalizing.

BTW We looked into AWS but didn't want to use an AWS only solution because of maximum size, costs, and the reusability of the solution.

Per disk. You can attach multiple disks to a single EC2 node.

So, RAID multiple EBS volumes and you have a larger disk.

That is quite honestly amazing turn around. Most people aren't in a position to get a replacement delivered from a vendor that quickly, but if you are, awesome. Again though, there's a big gap between simple, local storage (we could probably provide a tighter SLO/SLA on Local SSD for example) and networked storage as a service.

As someone else alluded to downthread: anyone claiming they can provide guaranteed throughput and latency on networked block devices at arbitrary percentiles in the face of hardware failure is misleading you. I don't disagree that you might feel better and have more visibility into what's going on when it's your own hardware, but it's an apples and oranges comparison.

> Most people aren't in a position to get a replacement delivered from a vendor that quickly

Back when I worked in enterprise services, it was a requirement that we had good support contracts — 1-, 4- or 8-hour turnarounds were standard.

If you're running a serious business, support contracts are a must.

Physically delivered, no matter customer location? Sign me up ;).

I'm not sure why you're so surprised, this is standard logistics management for warranty replacement services.

Manufacturer specifically asks customer to keep it informed where the equipment is physically located, and then prepositions spares to appropriate depots in order to meet the contractual requirement established when the customer paid them often a large amount of money for 4-hour Same Day (24x7x365) coverage for that device.

This isn't how hyperscale folks operate for the same reason Fortune 100's rarely take out anything more than third-party coverage when their employees rent vehicles, it becomes an actuarial decision, the # of 'Advance Replacement' warranty contracts and the $ involved, vs. buying a % of spares and keeping those in the datacenter then RMA'ing the defective component for refund/replace (on a 3-5 week turnaround time).

tl;dr - Operating 100-500 servers you should likely pay Dell and they'll ship you the spare and a technician to install it, operating >500 servers and you should do the sums and make the best decision for your business, operating >5000 servers and you probably want to just 'cold spare' and replace yourself.

Back when I worked in a big corp with an actual DC onsite we had similar contracts. I assume they worked anywhere in the US as we had multiple locations. IIRC they were with HP.

We had such a contract with Dell when I worked in HPC (at a large university). Since our churn was so high (top 500 cluster) we had common spare parts on site (RAM, drives) but when we needed a new motherboard it was there within 4 hours.

Now, these contracts aren't like your average SaaS offering. We had a sales rep and the terms of the support contract were personalized to our needs. I imagine some locations were offered better terms for 4 hour service than others.

As I learned long ago, never say no to a customer request. Just provide a quote high enough to make it worthwhile.

As nixgeek says, this is standard -- for a price.

That said I suspect most enterprises pay too much; as in their money might be better spent buying triple mirroring on a JBOD rather than a platinum service contract with a fancy all in one high end RAID-y machine.

One of the things I stress when talking to customers is that when one is moving to cloud, it's not just the business model that changes, but the architecture model.

That may sound like cold comfort on the face of it, but it's key to getting the most out of cloud and exceed the possibilities of an on-prem architecture. Rule #1 is, everything fails. The key advantage to a good cloud provider (and there are many) is not that they can deliver a guarantee against failure (as boulos stated correctly) but that they'll allow you to design for failure. The issue becomes when the architecture in the cloud resembles that which was on-premise. While there's still some advantages, they're markedly fewer, and as you said, there's nothing you can do to prioritize your fix.

They key to having a good cloud deployment is effectively utilizing the features that eliminate single points of failure so that the same storage controller failure that might knock you out in your on-prem can't knock you out in the cloud, even though the repair time for the latter might be longer. That brings its own challenges, but brings huge advantages when it comes together.

Disclosure: I work for AWS.

Most ppl just want to deal with one provider though. Meaning there has to be a middle man btw you and the customer.

By point of comparison, we had storage problems that went on for months or years. We had a vendor that was responsive to slas, but the problem was bigger than just random hardware failures, it was just fundamentally unsuited to what we were trying to do with it. That's the risk you take when you try to build your own.

In this case, it sounds like the cloud was fundamentally unsuited for what GitLab was trying to do with it. So definitely still a risk!

At the scale gitlab is talking about, it is usually better to source from a vendor that doesn't provide ultra-fast turnaround, and just keep a few spare servers and switches, so you can have 0-hour turnaround for hardware failure.

Get servers from Quanta, Wistron or Supermicro, and switches from Quanta, Edge-core or Supermicro. The $$$ you save vs a name-brand OEM more than pays for the spares. Use PXE/ONIE and an automation tool like Ansible or Puppet to manage the servers and switches, and you can get a replacement server or switch up and in service in minutes, not hours.

If you're moving out of the cloud to your own infrastructure, it makes sense to build and run similarly to how those cloud providers do.

I kinda disagree, see my other comment on logistical models, this isn't 5000+ system scale or even 500+ system scale.

There's non-trivial cost involved in simply being staffed to accommodate the model you propose, all of the ODM's have some "sharp edges" and you need to be prepared to invest engineering effort into RFP/RFQ processes, tooling and dealing with firmware glitches, etc.

Remember that 500-rack (per buy) scale is table stakes for "those cloud providers", it is their business, whereas GitLab is a software company. Play to your strengths.

In my experience, you'll be dealing with firmware glitches even with mainstream OEMs. You can avoid a lot of the RFP/RFQ and scale issues by going to a ODM/OEM hybrid like Edge-core, or Quanta. Or Penguin Computing or Supermicro. If you already have a relationship with Dell or HP, you probably won't get quite as good pricing, but they're still options.

I am shockingly biased (I co-founded Cumulus Networks) but working with a software vendor who can help you with the entire solution is very helpful.

The scale gitlab has talked about in this thread is firmly in the range where self-sparing/ODM/disaggregation make sense. I think 500 racks is a huge overestimate, I think the cross-over point is closer to 5 racks.

A ToR failure doesn't have to mean the end if you're willing to wire each server to two ToRs and duplicate traffic streams to both. It's a waste, but it's one way to achieve high reliability if you have customers willing to pay for it.

As someone on the private cloud team for a large internet company, dealing with storage problems is a nightmare that never ends. AWS is a walk in the park by comparison.

> See my note about SLAs and ToR failures. [...] but high-performance, guaranteed networked storage is just tricky

New job title: Networked Infrastructure Actuary

OTOH, solving the tricky parts in scalable ways is exactly the kind of unique selling point that cloud providers should offer.

> The OP is asking for guaranteed IOPS/latency SLA for which they're willing to pay HUGE money for by ROLLING THEIR OWN.

There is no guarantee of SLA in any distributed system. The best you can do is measure things and know what you'll get most of the time.

If you want SLA, you can make a single server with 10TB of memory as storage. That's solid choice! :D

I'm not sure we want to pay huge money. Right now it looks like our cloud hosting bill for 2 months (about $250k) can pay for the hardware to host 4x as much https://docs.google.com/spreadsheets/d/1XG9VXdDxNd8ipgPlEr7N...

How are you calculating cost to your organization to run your own hardware? With a cloud provider you're benefitting from their own engineering pooled across thousands of customers.

When you run your own hardware you have all the engineering you were already doing plus investing to upkeep and to improve your architecture.

As Google's boulos said, that's where the real costs are.

Indeed with metal you have less flexibility and much higher engineering costs that offset your savings. We think metal will be more affordable as we scale but that is not the reason for doing it. We do it because it is the only way to scale Ceph.

I know at least two 500TB+ clusters running on IaaS and don't think "only way to scale Ceph" is to buy and rack machines.

In an earlier comment you said EBS only goes to 16TB and that is "an order of magnitude less" than your requirement, however, thats per volume, you can attach many volumes in much the same way as servers have many disks.

Scale horizontally not vertically, add more OSD instances? With each you can attach a number of EBS or PD volumes which each IOPS characteristics that in aggregate are sufficient to service your workload?

If you want to avoid EBS or PD entirely, is there a reason you can't look at 'i2' or 'd2' instance types?

https://cloud.google.com/compute/docs/disks/performance https://aws.amazon.com/ebs/details/#VolumeTypes

At a fundamental level you're just moving the problem and trading managing metal (which is hard) for I/O guarantees.

"Why is this harder than you might expect?" - you stated elsewhere that you'll have Remote Hands do rack/stack. Providers like Equinix refer to this as "Smart Hands". Everyone who's managed a reasonable-sized environment finds this term highly ironic, as the technician can and will replace the wrong drive, pull the wrong cable, etc.

I've done an non-trivial amount of infrastructure 'stuff' (design, procurement, install, maintenance, migration) for some well-known companies, if you want to Hangout for an hour and pick my brain, gratis, my e-mail is in my profile.

My business partner and I ran a website (rubylane.com) for many years, just the 2 of us, colocated at he.net. With good hardware (we used Supermicro servers bought from acme.com), it's not a big deal. We mirrored every disk drive with hardware raid1, had all the servers connected in a loop via their serial ports, had the consoles redirected to the serial ports, and it was not much of a hassle. When we were first starting, we used cheap hardware and that caused us some pain. The other very useful thing we had setup is virtual IP addresses for all of the services: search engine, database, www server, image server, etc. The few times we ever had trouble with the site or needed to take a machine out of service, we could redirect its services to another machine with fakeip.

Recently I bought an old SuperMicro server on eBay, configured it with 2 6-way AMD Opterons, 3 8-way SATA controllers, and 32GB of memory. With 4TB 5700RPM drives in an 8-way software RAID6, it could do 800MB/sec. I realize it's not small file random I/O, but a blended configuration where you put small files on SSD and large files on spinning disk would probably be pretty sweet.

My intuition is that learning all the ins-and-outs of AWS, and how to react and handle all kinds of situations, is not that much easier than learning how to react with your own hardware when problems come up. Especially consider that AWS is constantly changing things and it's out of your control, whereas with your own hardware, you get to decide when things change.

If you can colocate physically close, it's a lot easier. Our colocation was in Fremont but our office was in San Fran, so it was a haul if we had to install or upgrade equipment. But even so, there was only 1 or 2 times in 7 years that we needed to spend 2 consecutive days at the colo. One of those was during a major upgrade where it turned out that the (cheap) hardware we bought was faulty.

Thanks. We plan to use a remote hands service to install new servers.

Ah, really? We are moved from Google Cloud, we just needed one machine with average IOPS to store our files (50-100gb only), but we are constantly hitting limits of IOPS, file upload for our users at some point became a nightmare. What's a problem with cloud when we pay for it 1k$+? Renting one server costs ~50$/mo and will cover everything. Only thing is needed is some adjustments in configuration. But, thanks to k8s we can roll out servers in a week. I am wonder now why we was needed to sit on clouds when everything works 10x times slower at 10x price?

What if your hardware fails?

What if you need to scale up (or scale down again)?

Making servers run as reliable as in cloud datacenters is really hard work and imposes additional cost. I.e. you need not one, but two or three datacenters with 2-3 times the amount of servers you actually use. Then you need admin staff who knows their work and keeps things running smoothly and reliably. You need not one but at least 3 of that staff because they might get sick or go on vacation.

Your cost savings probably comes from cutting corners. Depending on the structure of your applications, downtime requirements and recovery plans, that may even be OK. You don't always need a fleet of tanks to deliver a box of milk bottles.

Hardware fails? It will start on other node automagically. May be we will need to switch psql instance. What kind of additional cost? Do you ever hit something really awful with k8s on self-hosted servers? What can go wrong except losing node?

So, you have redundancy and failover at the application level. You don't need reliable servers then.

Reliability is with respect to some SLA; it could very well be that one would _like_ to timeout more quickly than can be reasonably expected of cloud infrastructure, but well within the capabilities of hardware itself.

> "Making servers run as reliable as in cloud datacenters is really hard work and imposes additional cost."

Not really. It's easy enough to have dedicated server hardware that runs just as smoothly as cloud hosted hardware. There are many options for doing so. The key is to pay for support.

For example, if you go with Microsoft or Red Hat or Ubuntu servers, you can pay for support contracts to get help from experts in configuring systems. Such options can work out cheaper than cloud hosting (depending on the IT infrastructure requirements), with the added benefit of having hardware more directly under your control.

What happens when you run into trouble with one of the servers? Like it's suddenly stopped responding and you can't SSH?

For my systems built on EC2, I might not need to do anything at all for typical hardware failures, if I've set up EC2 auto recovery. It transparently relaunches my instance on another server. If I'm not using auto recovery, then I might just stop and restart the instance, in which case I'm also migrated to another physical server if the first one wasn't working. It has the same identity, by the way: same IP address, same disk contents, and all that, and all the machine perceived was an OS reboot (or maybe kernel panic followed by reboot, depending on the failure).

For stateless systems I don't even need to bother with that. I'll just configure it to spin up a replacement instance if the desired number of servers I want to have online is not met because one of them failed. When I have 100+ servers in a fleet, this is really convenient. I don't need to keep track of them individually, I just say: "This is the image I'd like to run, and I want to have 100 of them". Hardware failures that would bring down a normal physical machine don't need to involve me at all.

The old server hardware that's broken is now in the hands of EC2 to repair or swap out, and my server's back up and running in minutes, possibly with no action on my part.

Is something like that easy to achieve with colocation and support offerings with those vendors? Genuine question - I've never operated in colo or worked with those vendors. I realize that colo facilities can take care of repairing and swapping servers for me, but the benefit I get from the cloud is that I can perform those actions in moments with an API, or they can happen automatically, and I don't need to engage other humans. I can't imagine spending my time coordinating with vendors, getting on the phone, opening support tickets, waiting for people to do things, etc... right now I can do everything at the speed of computing with APIs and automation. It'd be tough to give that up.

If you start running EC2 clusters, you're more in the "cloud storage" dominion and not really in the "self hosting" area anymore.

Not everybody needs that and not everybody who does need it also realizes it before a major failure strikes out one of their machines and there is no working failover and their one admin is not reachable and when they finally reach him he has to be flown in, then they need to wait for replacement parts, which all in all delays recovery by several days.

> "What happens when you run into trouble with one of the servers? Like it's suddenly stopped responding and you can't SSH?"

You've got plenty of options. Reboot the server (using a local login, as the server is hosted where employees/support staff are physically close to it), restore the server from a backup, etc...

Let's put it like this, how do you think companies managed before cloud servers? Do you think they just had the attitude of 'Oh damn the server has gone down, nobody can do any work today'? I'd put it to you that contingency plans existed long before cloud hosts did.

Out of band management gets you remote console access and fallback to a local technician if there's a hardware problem.

Do you need to store data?

If yes, how is it replicated over multiple datacenters?

If yes, does failover work flawlessly?

> "If yes, how is it replicated over multiple datacenters?"

Depends on the database engine used. For example...

https://msdn.microsoft.com/en-gb/library/ms151799.aspx

>"If yes, does failover work flawlessly?"

Again, depends on the database engine used. To use SQL Server as an example again...

https://technet.microsoft.com/en-us/library/ms189590(v=sql.1...

Traditional clustering with SQL Server is a huge pain in the ass. When it works (most of the time) it works well but failures can get hairy quick. There's tradeoffs but if you can make it work AlwaysOn is so much easier to deal with from an ops perspective.

> You don't always need a fleet of tanks to deliver a box of milk bottles.

A bottle of milk filled with Gold is worth about $800k.

By extension the 6-pack is $4.8M

If tanks can fit seamlessly in the budget, we shall give tanks a serious thoughts! :D

If your setup can run on a $50 server, you shouldn't use AWS/GCE ^^

Out of curiosity. What were you running? What was your setup? How much disk IOPS? and disk bandwidth used?

Are you sure that (just example) - https://www.hetzner.de/us/hosting/produkte_rootserver/ex41ss... is a weak server? Running same VM on AWS/GCE will cost 10x more.

OMG A server WITHOUT ECC memory. #fear

Let's not call that a server but a desktop computer please ^^

---

The point of the cloud is to manage MANY servers. If all you have is a single box, you don't need help to manage it, you don't need AWS/GCE.

If i can buy two desktops instead of one server then i can made a nice failover configuration instead of using just one server. Also as i know google and fb think that ecc is useless, isn't it?

Well, just order 50 of them and install k8s.

Failover is useless when you have already increased your chances of corrupting data. Even with ECC there's some degree of corruption; doing without is suicidal.

Google figured quite early in its life that RAM was the one component not to skimp on: http://research.google.com/pubs/pub35162.html

If you have an application where the performance and growth patterns are well known, cloud isn't a choice made for lowest cost. It may be best value for different reasons.

I've done ROI studies for several applications like that, and usually cloud has a higher total cost unless there are specific availability requirements or you don't have a facility that can meet a 99.9 SLA.

The key assumption is that you know a lot about the app and it's in a operating mode. If you're in a hyper growth mode, have fluctuating or seasonal demand, or you have no capital funds, cloud is a no brainer.

For sure, I think you can often save a decent amount of $$ with dedicated hardware. It does have downsides of course...

If your demand is 50% stable 50% fluctuating (say some base load + a big spike at US prime time), I still think you can win with a hybrid cloud... i.e. serve base load from a COLO, and serve spike load from the cloud. That does mean you need to configure at least 2 networks, but not a terrible idea from a DR standpoint anyway (Main DC fail? Push a button and run off the cloud until it is fixed)

This thinking (hybrid cloud for dynamic scale out) is going into our decision at GitLab and makes a lot of sense for us.

hardware provides so much headroom that it's not even funny to compare :) a good PCIE board will do 850K IOPS for reads for 10K (4TB). You can have a sane understandable setup. In our experience our clients on AWS had more downtime than on dedicated clusters. All major outages of public clouds have being due to control plane issues because it's too complex. Unless you are a major customer have fun trying to get things resolved with the cloud provider. At gitlub scale they would need 4 ops guys and some remote hands for hardware installs considering cloud pricing on bandwidth and storage and the cost of the ops team (+/- 24K month in Ukraine tops) they will not only get much better performance but will actually save decent amount of money.

I sense a collaboration oppurtunity between gcloud and gitlab might be benefitical, while google helps gitlab getting git running against your object storage ;) would be a win-win for both I guess!

"""For what it's worth, hardware doesn't provide an IOPS/latency SLA either ;)."""

Actually it really does for all practical purposes.

When it fails its SLA you replace it.

On the storage front, even enterprise grade SSDs with hundreds of thousands of 4k read and write IOPs set up in over-provisioned arrays won't give you a great SLA unless you really lowball it and say the SLA is 99th percentile latency / IOPS is 1/2 benchmarked and the hardware has to sustain that latency/IOPS for 99.99% (after benchmarking out to figure out cache vs sustained performance)

That's just storage, now you need to add so many layers on top of it. Like @boulos said, it is then your fault, but your customers still see the issues.

ToR failure? Tried googling it but it wasn't much help.

Top of Rack = the network switch that ties the servers on a rack to each other and provides a gateway to the rest of the datacenter.

I always recommend these:

https://scalableinformatics.com/assets/documents/Unison_Peta...

Surprisingly cost effective given the massive performance and support. Cloud is great for some things but not everything.

Thanks for the shout out! Without being a commercial, this high performance storage/analytics realm is what we focus on. We were demoing units like this: https://scalability.org/images/30GBps.png for years now. Insanely fast, tastes great, less filling. Our NVM versions are pretty awesome as well.

[edit]

I should point out that we build systems that the OP wants ... they likely don't know about us as we are a small company ...

https://scalableinformatics.com

and we do use gitlab

https://gitlab.scalableinformatics.com

...

Always happy to help ...

Thanks for using GitLab and posting in https://gitlab.com/gitlab-com/infrastructure/issues/727#note... This looks really interesting.

I did not realize they were on Azure until I read this comment. GitLab post did not mention it, why did you then?

I'm glad I wasn't the only one to notice! Literally the first thing the Google engineer does is mention Azure, while I had to go back to Gitlab's article all confused as I didn't notice at any point they were running on Azure.

I can't say it's a bad thing to do; I just can't help but notice how Google invests in social media participation. That's why they own the conversation in places like HN and can pull off this stuff.

What I fail to understand is, how does GCE or AWS tackle the issue described in the article? As far as I understand, their problem seems difficult to work around due to the nature of the Cloud (shared).

How would GCE be better than AWS or Azure at this? I would be really interested to know and I'm sure that'll be useful for other HNers with the same worries.

Disclaimer: I work for AWS.

To solve problems just like these, we offer EBS (elastic block storage) with provisioned IOPs guarantees. Essentially, you can get guaranteed IOPs if you need it for I/O intensive applications; up to 30,000 IOPs per EBS volume.

But, PIOPs EBS volumes wouldn't be my first recommendation. It sounds like what they really need is an elastic, scale-out filesystem with NFS semantics. We have Elastic File System, or EFS, which is exactly that. It's a petabyte scale filesystem that is highly available across multiple availability zones, and scales in IOPs and performance as it scales in size.

Their application should also look at leveraging S3 object storage, rather than NFS, because that is a highly distributed, highly available object storage system, that is likely to give better scalability, availability, and performance, than rolling your own Ceph infrastructure.

This is a great answer, thanks illumin8! (and cool nick too :D)

Technical details aside, the "buts", parentheses, and generally weird structure of this reply made it very confusing.

I personally believe that, when a prospect feels wronged or poorly served by a competitor, it's the company's responsibility to reach out to that prospect directly. Ideally 1-on-1, the company should aim to listen carefully to the prospect's concerns and not to immediately start spouting opinions or solutions. From there, an honest dialogue can take place which can form the basis of a sale. And, more importantly, a relationship.

Of course, if the goal is simply to castigate the competition or to ward off uncomfortable questions by implying the dissatisfied prospect is thinking poorly or emotionally, then a public forum post works better, I guess.

Sorry if you found my writing style confusing. I'm not looking to shame anyone. Instead, my hope was to counter the overly broad "It's clear we must not be in the Cloud" with my experience that this may be particular to their provider.

I'm not here trying to sell them on coming to Google. If they're interested, my contact info is in my profile. It's quite likely that the best option for them would be to return to AWS, as they have experience running there and EBS has improved a lot over the years.

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