Does anybody have any experience with a big enough and this kind of configuration, and what is the performance compared with SSD local disks? Intuitively I wouldn't expect a networked disk to be a viable solution for postgres, but seeing it proposed like this makes me think that maybe my intuition was wrong...
They're implemented like a software SAN, with dedicated network paths, and throughput/latency is very good. Not as good as local, but still good enough for most apps.
On Google Cloud, you do have to option of using a local SSD [1], but it comes with a bunch of limitations. It maxes out at 375GB (though you can allocate up to 8 per VM). They're somewhat expensive. They're not durable; if you stop the VM, the disk is lost. They're classified as "scratch disks" in the UI, which is a good indicator of their intended purpose.
Edit: Using a networked file system, however, is a bad idea.
NFS != SAN
The former is a shared file system accessible by multiple machines simultaneously.
The latter is a block device accessed over the network by a single machine at a time.
It's generally a bad idea to run a database on NFS as it'll be fine until it's not. Network block devices are fine though as it's just like a disk except it "plugs in" through your network jack rather than something like SATA.
I agree that NFS is a terrible idea for databases.
We (3 companies ago) used to use postgresql databases backed by a huge netapp filer.
Performance was as you would expect, horrible but tolderable. Why was it tolerable? Because high availability was more important than performance at the time and native HA wasn't in PostgreSQL yet. (8.1 had just come out)
The first DBA ever on staff was an absurdly knowledgable guy (and paid handsomely for being so knowledgeable) and his first and strongest recommendation was, in this order:
1) Upgrade to the latest PostgreSQL to get a better vacuum implementation.
2) Get the data off the filer.
I highly advise against it unless your application caches tremendously well.
To (inexactly) translate SAN/NAS into AWS terms for those that may not be familiar with these types of on-prem deployments: S3/EFS/Glacier is NAS–files are stored and retrieved over the network. EBS is SAN–the storage is exposed as a block level device over the network and appear as locally attached devices.
As a case in point, I've pushed greater than 600mb/s of simultaneous heavy read and write traffic to an AWS EBS volume with acceptably low mean latency, which is more than enough for many Postgres use cases, but there's definitely cases where even that level IO would be a major bottleneck.
GCP offers networked SSD, and performance is fairly good, but, as always, YMMV.
Disclosure: I work at Google on Kubernetes
It's a performance vs. availability/reliability tradeoff, and it's not a straightforward one.
> The example in this blog uses NFS for the Persistent Volumes, but any shared file system would also work (ex: ceph, gluster).
NFS is possible, but it's very easy to get the settings wrong, and it will depend on your specific NFS server whether or not you risk losing data in corner cases... I'd not consider NFS for a database for that reason without knowing precisely which NFS server and which version and testing that specific combination extensively (or verifying others have experience with exactly that combination).
It will be as slow as a block store, but most of the block stores offer up much simpler semantics that are much easier to verify if makes sense for a database workload (they need to store the blocks they claim to have stored, and that's pretty much what we care about; for the rest it's down to trusting a well tested local filesystem).
As an added note, the "any shared file system would also work" is patently false and horrible, dangerous advice, for a database deployment as it depends entirely on the file systems crash semantics in terms of what data is guaranteed to hit disk in a durable way, and whether or not there's any chance of writes being reordered etc.
The blog writes from the perspective of an on-prem deployment and suggests you could use NFS to provide a PersistentVolume to Kubernetes. While this is possible, it's probably not best practice, especially if a failure in your NFS will render all your nodes offline at once.