Messages in this thread | | | Date | Mon, 21 Nov 2005 21:31:14 +0100 | From | Lars Roland <> | Subject | Poor Software RAID-0 performance with 2.6.14.2 |
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I have created a stripe across two 500Gb disks located on separate IDE channels using:
mdadm -Cv /dev/md0 -c32 -n2 -l0 /dev/hdb /dev/hdd
the performance is awful on both kernel 2.6.12.5 and 2.6.14.2 (even with hdparm and blockdev tuning), both bonnie++ and hdparm (included below) shows a single disk operating faster than the stripe:
---- dkstorage01:~# hdparm -t /dev/md0 /dev/md0: Timing buffered disk reads: 182 MB in 3.01 seconds = 60.47 MB/sec
dkstorage02:~# hdparm -t /dev/hdc1 /dev/hdc1: Timing buffered disk reads: 184 MB in 3.02 seconds = 60.93 MB/sec ----
I am aware of cpu overhead with software raid but such a degradation should not be the case with raid 0, especially not when the OS is located on a separate SCSI disk - the IDE disks should just be ready to work.
There have been some earlier reporting on this problem but they all seam to end more and less inconclusive (here is one http://kerneltrap.org/node/4745). Some people favors switching to dmraid with device mapper, is this the de facto standard today ?
Examining the setup with mdadm gives: ------- dkstorage01:~# mdadm -E /dev/hdb /dev/hdb: Magic : a92b4efc Version : 00.90.02 UUID : 7edc2c10:6cb402e8:06d9bd91:57b11f01 Creation Time : Mon Nov 21 19:38:30 2005 Raid Level : raid0 Device Size : 488386496 (465.76 GiB 500.11 GB) Raid Devices : 2 Total Devices : 2 Preferred Minor : 0
Update Time : Mon Nov 21 19:38:30 2005 State : active Active Devices : 2 Working Devices : 2 Failed Devices : 0 Spare Devices : 0 Checksum : 9766c3ec - correct Events : 0.1
Chunk Size : 4K
Number Major Minor RaidDevice State this 1 3 64 1 active sync /dev/hdb
0 0 22 64 0 active sync /dev/hdd 1 1 3 64 1 active sync /dev/hdb -------
mdadm is v1.12.0.
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