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

[steve at linuxsuite.org]

> 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
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>>
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>