On Thu, Apr 17, 2008 at 11:47 AM, Bob Friesenhahn < [EMAIL PROTECTED]> wrote:
> On Thu, 17 Apr 2008, Pascal Vandeputte wrote: > > > > At the moment I'm seeing read speeds of 200MB/s on a ZFS raidz > > filesystem consisting of c1t0d0s3, c1t1d0 and c1t2d0 (I'm booting > > from a small 700MB slice on the first sata drive; c1t0d0s3 is about > > 690 "real" gigabytes large and ZFS just uses the same amount of > > sectors on the other disks and leaves the rest untouched). As a > > single drive should top out at about 104MB/s for sequential access > > in the outer tracks, I'm very pleased with that. > > > > But the write speeds I'm getting are still far below my > > expectations: about 20MB/s (versus 14MB/s in Windows 2003 with Intel > > RAID driver). I was hoping for at least 100MB/s, maybe even more. > > I don't know what you should be expecting. 20MB/s seems pretty poor > but 100MB/s seems like a stretch with only three drives. > > > I'm a Solaris newbie (but with the intention of learning a whole > > lot), so I may have overlooked something. I also don't really know > > where to start looking for bottlenecks. > > There are a couple of things which come to mind. > > * Since you are using a slice on the boot drive, this causes ZFS to > not enable the disk drive write cache since it does not assume to know > what the filesystem on the other partition needs. As a result, writes > to that disk will have more latency and since you are using raidz > (which needs to write to all the drives) the extra latency will impact > overall write performance. If one of the drives has slower write > performance than the others, then the whole raidz will suffer. See > "Storage Pools" in > http://www.solarisinternals.com/wiki/index.php/ZFS_Best_Practices_Guide. > > * Maybe this ICH9R interface has some sort of bottleneck in its > design or there is a driver performance problem. If the ICH9R is > sharing resources rather than dedicating a channel for each drive, > then raidz's increased write load may be overwelming it. > > If you are looking for really good scalable write performance, perhaps > you should be using mirrors instead. > > In order to see if you have a slow drive, run 'iostat -x' while > writing data. If the svc_t field is much higher for one drive than > the others, then that drive is likely slow. > > Bob > ====================================== > Bob Friesenhahn > [EMAIL PROTECTED], http://www.simplesystems.org/users/bfriesen/ > GraphicsMagick Maintainer, http://www.GraphicsMagick.org/ > > _______________________________________________ > zfs-discuss mailing list > zfs-discuss@opensolaris.org > http://mail.opensolaris.org/mailman/listinfo/zfs-discuss > Along those lines, I'd *strongly* suggest running Jeff's script to pin down whether one drive is the culprit: #!/bin/ksh disks=`format </dev/null | grep c.t.d | nawk '{print $2}'` getspeed1() { ptime dd if=/dev/rdsk/${1}s0 of=/dev/null bs=64k count=1024 2>&1 | nawk '$1 == "real" { printf("%.0f\n", 67.108864 / $2) }' } getspeed() { for iter in 1 2 3 do getspeed1 $1 done | sort -n | tail -2 | head -1 } for disk in $disks do echo $disk `getspeed $disk` MB/sec done ----------------------
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