Date: Wed, 21 May 2008 14:08:17 -0600 From: Scott Long <scottl@samsco.org> To: Chris Dillon <cdillon@wolves.k12.mo.us> Cc: freebsd-scsi@freebsd.org Subject: Re: Very poor performance from Dell/LSI Logic SAS 3000 series SATA/SAS RAID controller FreeBSD 6.3 Message-ID: <48348131.3040602@samsco.org> In-Reply-To: <20080521143051.17771kseoxrlhy7f@www.wolves.k12.mo.us> References: <4832C397.3090004@calorieking.com> <4832E0EE.3030402@samsco.org> <4832E6C2.7040205@calorieking.com> <48336EA0.3050109@samsco.org> <20080521143051.17771kseoxrlhy7f@www.wolves.k12.mo.us>
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Chris Dillon wrote: > Quoting Scott Long <scottl@samsco.org>: > >> For data reliability, you really don't want it enabled by default. The >> problem is that SATA/ATA performs so poorly without it that everyone >> turns it on and lives with the consequences. The tweak that I >> recommended puts it in line with what the FreeBSD ATA driver has been >> doing for years. > > Doesn't SATA NCQ solve this particular performance vs. reliability > problem since it safely allows multiple outstanding write requests? Of > course that means the SATA RAID controller would have to use NCQ on the > drives and would probably also need its own non-volatile cache. I've > always assumed this is how SCSI/SAS drives (with TCQ) perform as well as > they do without sacrificing data integrity. Yes and no. NCQ gets you 90% the way there, but the lack of an ordered tag operation in the NCQ protocol means that i/o streams can be starved, forcing you to do unpleasant i/o scheduling hacks. But yes, it helps quite a bit, and I have a prototype driver already working that supports NCQ and performs very well with write cache turned off. > > We recently bought a new HP DL380G5 server with a P800 SAS RAID > controller, MSA60 external drive shelf with 12 750GB SATA drives, > 11-drive RAID5 array w/ hot-spare (a few too many drives in a single > RAID5 array, I know, but I'm experimenting). The system is running > Windows Server 2K3 R2. Without telling the P800 to enable the SATA WC > (it has an option to do so, off by default), when doing a drag and drop > file copy of several very large files from the internal SAS array to the > external SATA array it writes 300MB/sec. I briefly enabled the > "Physical Drive Write Cache" on the controller just a few minutes ago > and ran another test and didn't notice any difference in write speed. I > can only assume from this that the P800 is using NCQ on the SATA drives. > The cache and queueing mechanism on most IOP raid cards will smooth over the performance problems with ATA/SATA, so your results aren't too surprising. Scott
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