Date: Thu, 09 Dec 2004 09:49:05 -0800 From: "Jin Guojun [VFFS]" <jin@george.lbl.gov> To: Mike Horwath <drechsau@Geeks.ORG> Cc: Bill Anderson <anderson@wks.uts.ohio-state.edu> Subject: Re: 2120S poor performance Message-ID: <41B89011.3040700@george.lbl.gov> In-Reply-To: <20041209170655.GH45512@octanews.net> References: <Pine.GSO.4.33.0412081120520.4974-100000@lennier.uts.ohio-state.edu> <20041209170655.GH45512@octanews.net>
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Mike Horwath wrote: >On Wed, Dec 08, 2004 at 11:51:21AM -0500, Bill Anderson wrote: > > >>I've got a 3x72g RAID5 array with U320 disks on an Adaptec 2120S >>controller under Freebsd 4.10. I'm getting about 25MB/s for sequential >>reads/writes (e.g. dd if=/dev/aacd0s1b of=/dev/null bs=32k). I've >>turned on write caching for the container (container set cache >>/write_cache_enable) and turned off the read caching, per previous posts >>to this list. I'm going to try setting hw.aac.iosize_max to 96k tonight >>to see if that helps. I'm currently using an IDE disk that gets about >>45MB/s, so I can hardly consider it an "upgrade" to switch to a 25MB/s >>U320 SCSI system. :/ >> >>I've also read that the 2120S is slow because of its design. I'm trying >>to figure out whether the performance can be increased significantly (I >>saw a posting of a linux user getting 37.5MB/s, which although still slow >>might be acceptable), or if I'm better off getting a new card. I'm >>thinking the latter is the case based on previous postings, but since it >>will probably be quite expensive to replace it, I wanted to get some more >>data. >> >>What performance should I be expecting from a decent U320 RAID5 >>controller? >> >>Has anyone gotten a 2120S to perform above 30Mb/s in FreeBSD? >> >>What's the cheapest controller that still gives reasonable performance? >>(If you could give a couple different ones, with their associated >>performance (under FreeBSD), or tell me where to find such information, >>that would be great) >> >> > >I know I left quite a bit of cruft above, but I don't see these kinds >of performance numbers you are seeing. > >First, SCSI does a lot with overlapping I/O and tagged queuing, only >the newest IDE (SATA) systems are starting to support such things. > >Second, SCSI disks run at a faster RPM most of the time (only the WD >Raptor hits the 10K mark), lowering seek time significantly. > >Third, my numbers: > >31MB/sec using > > dd if=/dev/aacd0s1b of=/dev/null bs=32k count=20000 > >34MB/sec using > > dd if=/dev/aacd0s1b of=/dev/null bs=64k count=20000 > >33MB/sec using > > dd if=/dev/aacd0s1b of=/dev/null bs=128k count=20000 > I do not remember where the original problem of 2120s was posted. The read in RAID 5 mode is 40-56 MB/s, where write rate is 5-13 MB/s. The most problem is at writing to RAID, average around 8 MB/s. SCSI buses self is Okay because doing multiple R/W without RAID can get maximum disk I/O. Soft RAID, like Vinum, also slows down disk array performance. SO, it sounds like that RAID design has big overhead to kill the performance. dd if=/dev/aacd0s1b of=/dev/null bs=128k count=20000 dev/null bs=128k count=20000 20000+0 records in 20000+0 records out 2621440000 bytes transferred in 61.651078 secs (42520587 bytes/sec) Adaptec guy told me that this is a design issue. One older model, which may be out of market, is performing better, but I would not expect a large difference as soft RAID do not give better performance. -- ------------ Jin Guojun ----------- v --- jin@george.lbl.gov --- Distributed Systems Department http://www.dsd.lbl.gov/~jin Lawrence Berkeley National Laboratory, Berkeley, CA 94720
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