John R Pierce wrote:
absolutely CRITICAL to any SAN implementations is that the storage controller (iscsi target, be it openfiler or what) remain 100% rock solid tsable at all times.
you can NOT REboot a shared storage controller without shutting all client systems down first (or at least unmounting all SAN volumes)
its non-trivial to implement a high availability (active/standby) storage controller with iscsi. very hard, in fact.
Dell have recently announced a product that may help a lot with this they call it Virtualized ISCSI devices see http://www.cns-service.com/equallogic/pdfs/WP910_Virtualized_iSCSI_SANs.pdf
commercial SANs are fully redundant, with redundant fiberchannel cards on each client and storage controller, redundant fiberchannel switches, redundant paths from the storage controllers to the actual drive arrays, etc. many of them shadow the writeback cache storage so if one controller fails the other one has any write cached blocks and can post them to the disk spindles transparently to maintain complete data coherency. Trying to achieve this level of 0.99999 uptime/reliability with commodity hardware and software is not easy.
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