High availability email server...

Pascal Gienger Pascal.Gienger at uni-konstanz.de
Fri Jul 28 17:49:31 EDT 2006

"David S. Madole" <david at madole.net> 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 

> 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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