I have karma to burn on this, so here goes: I worked for several years in VFX/HPC. 30k+ cpus and 15pbs of storage. Firstly with storage its very rare that people want actual block storage (unless you are hosting VMs, but thats so 2007.....) Yes, I know, openstack, but that's just fucking horrific, seriously just use netboot and be done with it. I've seen people do it inside new clustereing systems, but its really not…
Why isn't a fourth option being explored: local storage with async replication? Seems like it'd be fairly simple and fast, and no worse than non-clustered NFS regarding data integrity. I'm just talking from ignorance, so am I missing something?
The simplest storage, is a bunch of dumb servers (well beefy dumb servers) with some application aware scripts to move/copy the dataset.
A place I worked at had a wrapper around rsync that would split up the directory and spawn multiple rsyncs to do a parallel copy.
The Directory structure was effectively copy on write, so backup to the nearline was <15 minutes