On Monday 04 September 2006 1:28 am, Neil Brown wrote: > On Wednesday August 30, pwaldo@xxxxxxxxxxxxx wrote: > > Hi all, > > > > I have an IMAP mail server where mail messages are stored on a RAID1 > > array. The access on that array (/dev/md3) has seemed slow, so I did some > > investigating. "iostat -x /dev/hd[bd] /dev/md3" shows this: > > > > avg-cpu: %user %nice %system %iowait %steal %idle > > 14.34 47.03 13.99 19.64 0.00 5.00 > > > > Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s rkB/s wkB/s > > avgrq-sz avgqu-sz await svctm %util hdb 1.05 34.88 35.48 > > 2.60 1531.23 299.85 765.62 149.93 48.08 0.20 5.38 3.07 > > 11.69 hdd 0.70 34.83 41.08 2.65 963.12 299.85 481.56 > > 149.93 28.88 0.15 3.49 1.65 7.24 md3 0.00 0.00 > > 78.31 36.98 2494.35 295.85 1247.18 147.93 24.20 0.00 0.00 > > 0.00 0.00 > > > > > > > > > > Here is my /proc/mdstat for md3: > > > > md3 : active raid1 hdb1[0] hdd1[1] > > 12699264 blocks [2/2] [UU] > > > > > > Observations: > > - Stats for raw disks writes are similar > > - Stats for reads on hdd are about half that of hdd > > Yes.... odd. > > There shouldn't be any bias to one drive or the other. > When it scans for the best drive to use, it always starts from the > last one that was used, so there should be no bias to one or the > other. > > I assume they are identical drives? > dd if=/dev/hdXX of=/dev/null bs=1024k count=1024 > > give similar speeds for each? > > NeilBrown Hi Neil, They are different drives: root@mail:~# cat /proc/ide/hd[bd]/model WDC WD205BA IC35L020AVER07-0 The read speeds are different, 14% by my calculations: root@mail:~# dd if=/dev/hdb of=/dev/null bs=1024k count=1024 1024+0 records in 1024+0 records out 1073741824 bytes (1.1 GB) copied, 49.1775 seconds, 21.8 MB/s root@mail:~# dd if=/dev/hdd of=/dev/null bs=1024k count=1024 1024+0 records in 1024+0 records out 1073741824 bytes (1.1 GB) copied, 42.3739 seconds, 25.3 MB/s BTW, my kernel is 2.6.15-26 and mdadm is 1.12.0, running on Kubuntu 6.06. Thanks! Paul -- VGER BF report: H 0.00374821 - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
