# [OmniOS-discuss] iSCSI traffic suddenly comes to a halt and then resumes

Narayan Desai narayan.desai at gmail.com
Tue May 5 14:32:19 UTC 2015

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    And, if you don't have the luxury of discarding hardware and replacing it
    with a supported configuration, you might look at finding marginal drives,
    either via error counters displayed in iostat -En, or drives with really
    high service times (in iostat -xnz output). We found (on a similar setup),
    that being really aggressive about drive replacement helped a lot.

    If you have desktop sata drives, then the drive firmware is part of the
    problem. Desktop drives retry for quite a long time when they encounter
    errors, which produce really inconsistent performance profiles. When you
    aggregate into a raid set (including in ZFS) tail latencies really start to
    matter for performance, and the pool just starts going out to lunch for a
    long time. If you can figure out and replace the drive is causing the
    problem (even if it isn't causing any hard errors), the pool performance
    goes back to normal.
     -nld

    On Tue, May 5, 2015 at 4:21 AM, <mir at miras.org> wrote:

    > On 2015-05-05 09:46, Matej Zerovnik wrote:
    >
    >>
    >> We still kept our SATA hard drives in Supermicro JBOD with SAS
    >> expander and SATA drives.
    >>
    >>  Your problem boils down to using SATA disks in a SAS expander. Search
    > omnios user list and you will find numerous proofs that using SATA disks in
    > a SAS expander causes weird behaviors and instability.
    >
    > The fact is that SATA disks is unsupported in a SAS expander due to
    > incompatibility between command sets in SAS and SATA. As an example SATA
    > NCQ is not passed through the SAS expander which might could be the cause
    > of your strange iSCSI disconnects experienced on the client side.
    >
    > ----
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