Depends on how you use it, and what its for.

_most_ object storage is actually used as a pseudo filesystem (ie S3 et al) because a shared, fast & reliable filesystem are vanishingly rare.

Apart from openstack (and I've never seen a successful deployment of it outside of rackspace) most use cases I've seen involve either bolting on a NFS head, or some other filesystem to ceph and serving it publicly.

which is frankly not all that great. I like the _idea_ of ceph, but I don't want to have to support it. Like Nexenta, it seems great, but it soon hurts during crunch.

What I like about GPFS is that it allows you to join up large amounts of block storage, regardless of the underlying fabric.

Everything has a hook, so if a file has been created/updated/moved/deleted/metadata changed, you can attach a script to that action. There is an inbuilt HSM, which allows you to shuffle files about based on their content: raw footage? move it to the spinny disk array, final deliverables? move it to the storage based in the other country. File bigger than 1TB, and hasn't been touched in two weeks, sure you can kick it out on to tape.

crucially because its all one name space, the end user doesn't have to care about where the file is, the system takes care of that based on rules.

The best part is, there are no special tricks needed for the end program, its just standard file io.

However it is one global system, which is it's downside. for pure uptime its better to have an array of file servers, to limit the blast radius, but then you don't get the goodness

Is there a short summary of which problems are solved by which filesystem?

On the interwebs? No idea. Mine would be:

GPFS is excellent as a clustered filesystem backing a number of servers that need high-throughput, low latency, coherent storage. It's block-oriented.

Ceph is a SAN replacement: can saturate 100 GBps switches with massive parallel throughput. Object based, can also serve up block and (recently, with limits) cooked filesystem.

Gluster is a distributed filesystem - easy to set up and configure, some performance limitations, file rather than object or block oriented.

GPFS is very much file oriented - there's iSCSI target support but I'd be surprised if anyone really used it.

Ceph can provide block (mostly used for VMs), object and file targets, in that order of maturity.

Gluster is sort of a metafilesystem, aggregating some number of underlying filesystems - file being the operative word.

I'm referring to the FS primitives. GPFS presents a POSIX FS, but it's primitive is blocks. Ceph is an object primitive (RADOS) and can present it a number of ways. And Gluster is based around files as primitives, which gives some interesting strengths and weaknesses.

>Ceph can provide block (mostly used for VMs), object and file targets, in that order of maturity.

That's a little bit backwards. Ceph's block storage is actually built upon objects internally.