Date: Sun, 25 Apr 1999 09:31:54 -0400 (EDT) From: Mikhail Teterin <mi@kot.ne.mediaone.net> To: ken@plutotech.com (Kenneth D. Merry) Cc: dnelson@emsphone.com, freebsd-scsi@FreeBSD.ORG Subject: Re: writing slower with SoftUpdates Message-ID: <199904251331.JAA04525@kot.ne.mediaone.net> In-Reply-To: <199904250636.AAA49618@panzer.plutotech.com> from "Kenneth D. Merry" at "Apr 25, 1999 00:36:51 am"
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Kenneth D. Merry once stated: mi: WCE was ON on both drives: mi: Checking SCSI drives for write-cache: mi: <SEAGATE ST39102LW 0006> at scbus0 target 8 lun 0 (pass0,da0) mi: <SEAGATE ST39102LW 0006> at scbus0 target 9 lun 0 (pass1,da1) mi: I disabled WCE on both and re-ran the iozone tests. No noticable mi: changes from the previous numbers... What really bothers me, is the mi: fact that reading speed speed is consistently only 13-14Mb/s on one mi: disk, while it is 17-18 (same as writing) on the other. => = camcontrol defects -u 0 -f phys -G => Got 0 defects. => camcontrol defects -u 1 -f phys -G => Got 0 defects. => 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. The difference (for reading) is 13-14Mb vs 17-18Mb per second -- kind of huge for seemingly identical drives. =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? This is on a very recent -stable... I'm going to update it to the very latest and retry... => 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. The two 256Mb paging areas I have, are also on the identical locations on the disks, but they are not even touched having 128Mb of RAM... =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? Not at all... => => 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*) Thanks! -mi To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-scsi" in the body of the message
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