# [OmniOS-discuss] How bad are these controller / io errors??

steve at linuxsuite.org steve at linuxsuite.org
Wed Aug 21 22:53:03 UTC 2013

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    > SATA drives behind SAS expanders have a pathological error case.  If a
    > drive encounters errors and it needs to be reset then the entire set of
    > drives will take the reset.  If any io is in flight this will error as a
    > result often causing another reset.  The result can best be described as a
    > cascade failure.
    >
    > There may be things software can do to mitigate this but experience is
    > that it doesn't.

            Hmmm..... I have put.

                allow-bus-device-reset=0;

          In sd.conf

          as it seemed to mitigate that problem?

    >
    > So just because the array is working fine now does not mean that it won't
    > fail tragically when the first problems occur.
    >
    > I have personal experience with this failure mode.
    >
    > As a result I strongly discourage the use of SATA drives unless they are
    > directly connected to the hba without any expanders or port multipliers.
    >
    > You ignore this advice at your own risk.  Don't penny pinch on the drives
    >  It ALWAYS costs you in the long run.
    >

             The advice in this thread, wrt SATA vs SAS, has been my thoughts
    and position
    for a while based on my initial research. I was required to explore and
    verify this option
    simply because of the significant economic  benefit if it was possible.
    Thanks for your
    input. I will use this to make my case

        So now I just need some cheap SAS drives ;-)

        thanx - steve

    > Sent from my iPhone
    >
    > On Aug 19, 2013, at 4:25 PM, steve at linuxsuite.org wrote:
    >
    >>> Can't agree more here. Desktop firmwares are designed to try harder to
    >>> never return an error.  While this is what home users want, it's an
    >>> anathema to large configurations with redundancy where you would prefer
    >>> to
    >>> just get the error so you can handle it - usually by doing the op on
    >>> another drive.
    >>>
    >>> Use enterprise drives if you love your data and your ability to access
    >>> it.
    >>
    >>        Yes I know, I know....  Desktop hardware sucks. Didn't know there
    >> was
    >> Enterprise (ie none Desktop) SATA. Perhaps the solution is to  partition
    >> the data and do "deep" storage that never gets read on large bulk SATA
    >> and
    >> then have a smaller SAS pool for the often read/written stuff.
    >>
    >>      Anyway, large storage rollouts will always be looking for
    >> the cheapest solution. Even if it isn't perfect. I do backups
    >> to a SATA pool (behind SAS expanders) with zfs send,.. no problems
    >> errors
    >> whatever YET!!
    >> (cross fingers)
    >>
    >>       -steve
    >>
    >>>
    >>> Sent from my iPhone
    >>>
    >>> On Aug 19, 2013, at 2:47 PM, Eric Sproul <esproul at omniti.com> wrote:
    >>>
    >>>> On Mon, Aug 19, 2013 at 5:35 PM,  <steve at linuxsuite.org> wrote:
    >>>>>    4T SATA  here
    >>>>>
    >>>>> http://www.newegg.com/Product/Product.aspx?Item=N82E16822178338
    >>>>>
    >>>>>         are $179
    >>>>
    >>>> That's a desktop drive, not nearline enterprise, so it's
    >>>> apples-oranges.  You get what you pay for.  Desktop drives can take
    >>>> much, much longer to respond to commands, leading the HBA/expander to
    >>>> declare them dead and reset them, and the rest is history.
    >>>>
    >>>> Avoid desktop parts.  :)
    >>>>
    >>>> Eric
    >>>> _______________________________________________
    >>>> OmniOS-discuss mailing list
    >>>> OmniOS-discuss at lists.omniti.com
    >>>> http://lists.omniti.com/mailman/listinfo/omnios-discuss
    >>
    >> _______________________________________________
    >> OmniOS-discuss mailing list
    >> OmniOS-discuss at lists.omniti.com
    >> http://lists.omniti.com/mailman/listinfo/omnios-discuss
    >

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