I understand it completely, and I vehemently disagree with everything about it. Providing networked block storage for virtual disks on top of NFS is a recipe for disaster and performance degradation. Just because "everyone" does it doesn't make me like it any more. Using redundant local disk (preferably with ZFS) gets around this problem. Blocks are actually blocks and failures and performance issues are confined to one node.
> Additionally, by having the sort of architecture being presented, you can do things like live migrations of VMs, which is useful when the underlying OS needs to be brought down for maintenance.
I find live migration to be a hack. Once again, solving the wrong problem at the wrong level.
> There are quite a few places where they just need a few servers, and going to your idea just makes things more expensive and more complicated.
Local disk with appropriate backups and application level failover makes a lot more sense and is fundamentally less complicated.