I don't understand why this is being used over say librados + librbd from Ceph. This seems like an awful lot of work to get the same functionality that Gluster/Ceph already have. Is there something I'm missing here?
Backed by etcd. Today etcd is a well tested and widely used consistent store with users like Kubernetes, Flannel (now Canal), Fleet, SkyDNS and many others. Building something like etcd requires tons of testing and etcd is becoming the solid go to for this category of distributed problems.
Easy to work on code base. Building an OSS community around a complex technology is really hard. It shouldn't be underestimated that a code base that can be built on OS X, Linux, and Windows will have an advantage in getting people involved and maturing the project.
Designed for other storage application. Torus is backed by a distributed storage interface that is exposed via gRPC (with the opportunity for language bindings in lots of languages). Our hope is to let people build write-ahead log systems, object systems, or filesystems on top of this abstraction.
Flexibility built into the storage layer. Over time we want people to implement different hash maps or explicit configuration of storage layout. This is an abstraction that we have today and intend to build out over time with feedback from users.
Happy to answer more questions. This is a young project and we look forward to working with people and hearing about what they want out of a storage system. Overall, we want to build something with folks that is easy to work on and backs itself with technologies that are getting good operational understanding in the "Cloud Native" space.
To me at least, having it "backed by etcd" is a big red flag, not a feature.
So, this company is trading away stuff like that for custom components and Etcd? And for a component focusing on integrity and availability? Huh?
I've managed to lose data with Etcd
Being built atop something else doesn't mean it inherits all the stability of the underlying system; it's an upper bound not a lower bound.
Thinking about it further, I think I can guess at what's going on here. The key observation is that there's no sync() at the block device level. It's a filesystem operation; block devices don't see it. Sure, there are queue flags and FUA and such, but those are different (and I'm not sure any of those exist in NBD). Where is this sync() path? I'm guessing it's internal on the data servers, to deal with data that's being buffered there. With both replication and erasure coding, correct recovery requires exact knowledge of what has been fully written where, and that's the kind of metadata I suspect is being put in etcd. There's not even necessarily anything wrong with it, unless updating that information only on sync() means that supposedly durable writes since the last (unpredictable to the client) sync could be lost on failure. I hope that's not the case.
Maybe I'll find time, in the midst of my work on an actual production-level distributed filesystem, to look at the code and see if my guess is correct.
> All writes up until a sync are effectively anonymous until a sync().
"Anonymous" means nothing in this context. Do you mean non-durable? First, please use the correct term. Second, if that is what you mean then you're probably doing it wrong. File writes are allowed to be asynchronous (unless O_SYNC and friends). Block device writes are expected to be synchronous, or at least to preserve order. This is exactly the kind of thing that needs to be thoroughly thought out before code is even written, and that thinking should be spelled out somewhere for people to help make sure all the nasty corner cases are covered. Your cart is way before your horse.
For Etcd I'm of two minds. I like its simplicity. On the other hand, I have had far more problems with Etcd than I've ever had with e.g. Consul (though I dislike Consuls "and the kitchen sink" approach), up to and including data loss and more than once having to re-initialise clusters. I'm a couple of years of no further problems at least a way from trusting Etcd with my data.
For this? They have to have very compelling stories for why they couldn't e.g. modify Ceph or Gluster to achieve whatever it is that they want. And it's no clear what they want. Gluster for example is built as a stack of pluggable translators that is relatively easy to extend.
Even if they have a credible and compelling story for why we need something else, it will take years of production use by others before I'd trust any data to a new distributed file system.
Gluster and Ceph have those years. I've had a Gluster volume running without maintenance or data loss for more than five years. Even then it took several years before I truly started to trust it.
Gluster had many issues too when it was a young project, but they were fixed many years ago. I don't doubt that Etcd too will become solid enough for me to trust, but looking at part of the docs [1] we still have "gems" such as "Permanent Loss of Quorum Requires New Cluster" (you don't lose your data to that one, but it's painful nevertheless).
And yes, I've run into that one. Not "permanent" as in "we could never recover the machines in question", but "permanent" as in "we're not going to be able to get this sorted fast enough, so let's fail everything over". Everything else we run can handle that scenario easily. We know it means consistency issues, but if you run into that situation we have taken the decision that they are acceptable and will be resolved later if necessary. The last thing I need in a scenario like that is for some critical component to just refuse to run without requiring lots of manual intervention.
All we'd like would be to be able to say "ok, drop all the other members and pretend all is well, and yes we know what we're asking". There are a number of gotcha's like that with Etcd that sounds find until they bite you in the ass.
They'll resolve these things eventually, but storage is the very last place I'd be willing to take risks with it. So until they have years of track record of running flawlessly, with less hassle than Gluster or Ceph, and substantial advantages, I'll see it as the dangerous choice.
[1] https://coreos.com/etcd/docs/latest/runtime-reconf-design.ht...
How many separate data centres do you want me to host in? Two is certainly insufficient, as if the data centre with the majority of Etcd nodes now falls of the network, you're SOL.
Three? Think you can't have two fall of face of the earth the first time? Been there. Redundant connections doesn't always help if there are major external connectivity issues and you don't have multi-million dollar budgets for connectivity alone.
Most small to mid size companies do not have the budget to run a system that is sufficiently redundant to be able to guarantee that they won't sooner or later be in a situation where either 1) the most viable partition is the minority, or 2) the Etcd cluster is centralised enough that too large parts of the cluster can loose access to it. When fighting large scale failures is the last time where you want to have to fight your tools to be able to convince them that you know what you're doing.
For those kind of situations, Etcd's lack of support for more fine-grained control of consistency or for intentionally breaking apart the cluster and letting them continue to operate independently when you know what you're doing basically makes it unsuitable for running multi-data centre clusters for anything important.
Which basically means any tools that assumes a single underlying Etcd cluster is appropriate as storage, for, say, a cluster scheduler (cough) becomes an inappropriate tool for those kind of setups.
And it generally seems that, when they say "composable modular tools", one should read "includes dependencies on the rest of our stack". This isn't intended as harshness. It is just that every time a tool from COS seems interesting enough to look in to, it turns out that I wouldn't be investing in a tool, it would be investing in an ecosystem that duplicates a ton of what I'm already managing.
https://en.wikipedia.org/wiki/Clustered_file_system#Distribu...
I write this not as storage religion (of which there's far too much), but to warn away those who haven't experienced the many kinds of data (and stomach lining) loss that come with being a Lustre admin.
http://sector.sourceforge.net/
I swore I added it to the Wikipedia links. I'll have to do it again, I guess.
(disclaimer: I'm an engineer there...)
I thought Elasticsearch was open-sourced, and the GitHub repo says Apache v2. What am I missing here?