Re: openfiler (was: using CentOS as an iSCSI server?)

[John R Pierce <pierce@xxxxxxxxxxxx>]

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. 

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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