We're currently designing a ZFS fileserver environment with iSCSI based
storage (for failover, cost, ease of expansion, and so on). As part of
this we would like to use multipathing for extra reliability, and I am
not sure how we want to configure it.
Our iSCSI backend only supports multiple sessions per target, not
multiple connections per session (and my understanding is that the
Solaris initiator doesn't currently support multiple connections
anyways). However, we have been cautioned that there is nothing in
the backend that imposes a global ordering for commands between the
sessions, and so disk IO might get reordered if Solaris's multipath load
balancing submits part of it to one session and part to another.
So: does anyone know if Solaris's multipath and iSCSI systems already
take care of this, or if ZFS already is paranoid enough to deal
with this, or if we should configure Solaris multipathing to not
load-balance?
(A load-balanced multipath configuration is simpler for us to
administer, at least until I figure out how to tell Solaris multipathing
which is the preferrred network for any given iSCSI target so we can
balance the overall network load by hand.)
Thanks in advance.
- cks
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