Date: Sun, 25 Apr 1999 00:36:51 -0600 (MDT) From: "Kenneth D. Merry" <ken@plutotech.com> To: mi@kot.ne.mediaone.net (Mikhail Teterin) Cc: dnelson@emsphone.com, freebsd-scsi@FreeBSD.ORG Subject: Re: writing slower with SoftUpdates Message-ID: <199904250636.AAA49618@panzer.plutotech.com> In-Reply-To: <199904250458.AAA03413@kot.ne.mediaone.net> from Mikhail Teterin at "Apr 25, 1999 0:58:34 am"
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Mikhail Teterin wrote... > Kenneth D. Merry once stated: > > => > > WCE was ON on both drives: > => > > > => > > Checking SCSI drives for write-cache: > => > > <SEAGATE ST39102LW 0006> at scbus0 target 8 lun 0 (pass0,da0) > => > > <SEAGATE ST39102LW 0006> at scbus0 target 9 lun 0 (pass1,da1) > > => > > I disabled WCE on both and re-ran the iozone tests. No noticable > => > > changes from the previous numbers... What really bothers me, is the > => > > fact that reading speed speed is consistently only 13-14Mb/s on one > => > > disk, while it is 17-18 (same as writing) on the other. > > =Try the physical sector format: > > = camcontrol defects -u 0 -f phys -G > Got 0 defects. > camcontrol defects -u 1 -f phys -G > Got 0 defects. > > =To get both: > > camcontrol defects -u 0 -f phys -PG | wc -l > Got 868 defects: > 868 > camcontrol defects -u 1 -f phys -PG | wc -l > Got 141 defects: > 141 > > Khmm, the second disk is indeed faster for writing and a LOT faster > for reading. Does this number of defects justify an exhange request > -- we just bought both disks? I don't think it's too far out of line for a 9 gig disk, but I suppose that could be one possible explanation for the speed difference. What happens when you read off the raw device, instead of from the filesystem? It might be nice to elminate some of the VM system from the equation. Also, is this on -current or -stable or what? > Why do SoftUpdates slow things down on both disks, anyway? With > and without WCE -- the numbers don't change noticeably... Well, perhaps there's some sort of VM problem that's causing the soft updates slowness? I really don't know what's going on. I've seen instances where having both softupdates and write caching enabled would cause variable performance on disks. But that variable performance would usually go away if I disabled one or the other. In this case, you've tried disabling write caching and it doesn't affect the results. So, that seems to point to maybe some sort of VM-type problem. Is iozone eating a lot of CPU time when you run benchmarks? > => The machine is 350MHz PentumII with 128Mb of 100MHz RAM. The disks > => are LVD being the only targets on the LVD outlet of Adaptec 2940U2W. > > =One other thing to look at is where you are on the disk. I/O > =performance will be better on the outer diameter tracks. > > I know, but the partitions are identical: > > mi@labservn:~ (95) mount | grep /tmp > /dev/da0s1e on /tmp (local, soft-updates, writes: sync 4 async 8014) > /dev/da1s1e on /var/tmp (local, soft-updates, writes: sync 23 async 4801) > mi@labservn:~ (96) ( disklabel da0 ; disklabel da1 ) | grep ' e:' > e: 1048576 655360 4.2BSD 0 0 0 # (Cyl. 963*- 2505*) > e: 1048576 655360 4.2BSD 0 0 0 # (Cyl. 963*- 2505*) Hmm, I suppose that pretty much rules out that possibility. I doubt that you'd see too much difference even if you were writing at the beginning of one 512MB partition and at the end of the other on a 9G disk. Ken -- Kenneth Merry ken@plutotech.com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-scsi" in the body of the message
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