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@xxxxxxx>
"We can't solve today's problems by using the same thinking we
used in creating them." - Einstein
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