I have to correct an error in perspective, or at least in the wording of it, in the following, because it affects how people see the big picture in trying to decide how the filesystem types in question fit into the world: >Shared storage can be more efficient than network file >systems like NFS because the storage access is often more efficient >than network access The shared storage access _is_ network access. In most cases, it's a fibre channel/FCP network. Nowadays, it's more and more common for it to be a TCP/IP network just like the one folks use for NFS (but carrying ISCSI instead of NFS). It's also been done with a handful of other TCP/IP-based block storage protocols. The reason the storage access is expected to be more efficient than the NFS access is because the block access network protocols are supposed to be more efficient than the file access network protocols. In reality, I'm not sure there really is such a difference in efficiency between the protocols. The demonstrated differences in efficiency, or at least in speed, are due to other things that are different between a given new shared block implementation and a given old shared file implementation. But there's another advantage to shared block over shared file that hasn't been mentioned yet: some people find it easier to manage a pool of blocks than a pool of filesystems. >it is more reliable because it doesn't have a >single point of failure in form of the NFS server. This advantage isn't because it's shared (block) storage, but because it's a distributed filesystem. There are shared storage filesystems (e.g. IBM SANFS, ADIC StorNext) that have a centralized metadata or locking server that makes them unreliable (or unscalable) in the same ways as an NFS server. -- Bryan Henderson IBM Almaden Research Center San Jose CA Filesystems -- Linux-cluster@xxxxxxxxxx http://www.redhat.com/mailman/listinfo/linux-cluster
