Raj, on 06/12/2010 03:17 AM wrote:
Nicholas A. Bellinger <n...@...> writes:
Btw, just for those following along, here is what MC/S and ERL=2 when
used in combination (yes, they are complementary) really do:
http://linux-iscsi.org/builds/user/nab/Inter.vs.OuterNexus.Multiplexing.pdf
Also, I should mention in all fairness that my team was the first to
implement both a Target and Initiator capable of MC/S and
ErrorRecoveryLevel=2 running on Linux, and the first target capable of
running MC/S from multiple initiator implementations.
But the end result is what? open-iSCSI still doesn't have the MC/S even though
it is useful?
The end result is that any driver level multipath, including MC/S, is
forbidden in Linux to encourage developers and vendors to improve MPIO
and not to try to workaround problems in it by their homebrewed
multipath solutions [1]. As the result of this very smart policy, Linux
MPIO is in a very good shape now. Particularly, it scales with more
links quite well. In contrast, according to Microsoft's data linked in
this list recently, Windows MPIO scales quite badly, but Linux MPIO
scales similarly as Windows MC/S does [2]. (BTW, this is a good evidence
that MC/S doesn't have any inherent performance advantage over MPIO.)
But we are on the Linux list, so we don't care about Windows' problems.
Everybody are encouraged to use MPIO and, if have any problem with it,
report it in the appropriate mailing lists.
Vlad
[1] Yes, MC/S is just a workaround apparently introduced by IETF
committee to eliminate multipath problems they see in SCSI inside their
_own_ protocol instead of to push T10 committee to make the necessary
changes in SAM. Or, because a lack of acceptance of those problem from
T10 committee. But I'm not familiar with so deep history, so can only
speculate about it.
[2] The Windows MPIO limitations can well explain why Microsoft is the
only OS vendor pushing MC/S: for them it's simpler to implement MC/S
than to fix those MPIO scalability problems. Additionally, it could have
a future marketing value for them: the improved MPIO scalability would
be a big point to push customers to migrate to the new Windows version.
But this is again just a vague speculation ground. We will see in the
future.
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