Re: OT: sas controllers/expanders and "desktop" drives?

[Bill Davidsen <davidsen@tmr.com>]

Matt Garman wrote:
> On Sat, Mar 20, 2010 at 11:34:19AM -0400, Bill Davidsen wrote:
>   
>> Matt Garman wrote:
>>     
>>> For example, from the FAQ for that SuperMicro chassis[3]:
>>>
>>>    Question: We want to use the new Seagate 1.5TB ST31500341AS
>>>    drives in combination with a storage solution based on your
>>>    846TQ chassis, is this compatible?
>>>
>>>    Answer: This ST31500341AS hard drive is designed to be a
>>>    Desktop type hard drive, not an Enterprise hard drive which
>>>    is needed in this setup.  We don't recommend this
>>>    combination, so please use the Seagate 1TB ST31000340NS drive
>>>    instead. This drive is an Enterprise drive and validated for
>>>    our 846TQ chassis.
>>>
>>> In short, we want to build a server with 24 drives.  The desktop
>>> drives are significantly cheaper than the enterprise drives.  But
>>> getting 24 ports is cheapest with these SAS controllers +
>>> expanders.
>>>       
>>  
>> I have the feeling that what they meant is that the drives have
>> firmware intended for desktop use and will not work well in RAID
>> usage. This has been discussed here before, the desktop drives
>> have firmware which tries repeatedly to recover data on a failed
>> read, and which therefore may hang for 20-30 sec before reporting
>> an error or finally returning the data without an error
>> indication.
>>     
>
> That makes sense.  For what it's worth, I found out that the
> expander chip on the SuperMicro 846 case is the LSI SASx36[1].
> (Note that there are several versions of this case; the E1 and E2
> are the ones that have the expander.  The TQ version doesn't have
> the expander chip.)
>
>   
>> Until/unless Neil changes his idea that timeout should be in the
>> driver or the driver, these drives work poorly with RAID.
>>     
>
> For this particular application, my requirements are a little
> different---I actually just want a bunch of individual drives; I
> won't be using RAID.  (But there seems to be a lot of folks on this
> list with a wide range of hardware experience, and I was hoping to
> catch someone with experience with this particular configuration.)
>
> Anyway, we went ahead and ordered the hardware---LSI SAS3081E-R
> card, case with the LSI SASX36 expander, and both WD Green and
> Samsung EcoGreen drives (both desktop class).  I'll be able to
> follow up shortly and report how well this configuration works (or
> doesn't) for standalone usage.
>
> As for RAID usage (md or hardware): just to be clear, my
> understanding is that the biggest problem is that, even if the
> desktop drives work fine for non-RAID use, they'll still be
> "difficult" in an array.  That is, they take too long to report
> errors, and thus get kicked out of the array.
>
> >From my perspective, this isn't a true hardware incompatibility;
> it's a software (or firmware) "mismatch".  If this is correct, then
> the "real" answer to the FAQ I copied above is more nuanced.  The
> current answer should be qualified with "for use in a RAID", and
> then go on to suggest that the drives should be ok for standalone
> use.
>   

See the information provided by Randy Terbush on this, you may be able 
to just change the ERT if you have the right drives.

-- 
Bill Davidsen <davidsen@tmr.com>
  "We can't solve today's problems by using the same thinking we
   used in creating them." - Einstein