"David S. Madole" <david@xxxxxxxxxx> wrote:
That's just not true as a general statement. SAN is a broad term that applies to much more than just farming out block devices. Some of the more sophisticated SANs are filesystem-based, not block-based. This allows them to implement more advanced functionality like cross-platform sharing of volumes, simultaneous mounts of volumes from different hosts, backups (and single-file restores) performed by the SAN system, pooling of free space, transparent migration to offline storage, etc., etc., etc.
In my "classical" view a SAN is a network used for storage applications to give a view on shareable block devices. There are hardware applications giving access to the same filesystem in a shareable manner (as GFS or ocfs) but this is software logic in the filesystem and firmware level and not in the classical SAN components like JBOD arrays, RAID controllers and FC or IP switches.
In the Apple case we need to distinguish Apple XSAN Harddisk chassis and the XSAN software. The XSAN software seem to give you a special filesystem for SAN issues (at least I read this on their webpage). So if Apple says that this is not suited well for many small files I would not use it for that.
Another instance of a SAN filesystem that I do happen to be familiar with is IBM's: http://www-03.ibm.com/servers/storage/software/virtualization/sfs/index.h tml
Also this filesystem lives above the FCP (Fiberchannel) protocol forming a filesystem including multipathing elements and concurrent access strategies. Still you have to distinguish the block-level access to SAN devices and the filesystems build above them. It is true that "SAN" is marketing speech for all kind of things.
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