From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bill Davidsen Subject: Re: OT: sas controllers/expanders and "desktop" drives? Date: Sat, 20 Mar 2010 13:34:50 -0400 Message-ID: <4BA5073A.1030802@tmr.com> References: <20100317143602.GA18298@septictank.raw-sewage.fake> <4BA4EAFB.1050302@tmr.com> <20100320164748.GA31221@septictank.raw-sewage.fake> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20100320164748.GA31221@septictank.raw-sewage.fake> Sender: linux-raid-owner@vger.kernel.org To: Matt Garman Cc: linux-raid List-Id: linux-raid.ids 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 "We can't solve today's problems by using the same thinking we used in creating them." - Einstein