[RndTbl] RAID5 rebuild performance

Adam Thompson athompso at athompso.net
Thu May 19 14:12:06 CDT 2011

Look back in dmesg output for the RAID module speed tests, notice which one was selected, and divide that number by 2.  There's your theoretical bottleneck on the CPU.
Take the minimum sustained disk/channel/controller throughput, factor in interrupt latency, device driver efficiency, etc. and make a rough guess as to the overall throughput.
Consider that md code seems to have a lot of write barriers for safety -  so even a rebuild will aspens much of its time waiting for the disk to sync().
All in all, I think your numbers are probably reasonable.

Kevin McGregor <kevin.a.mcgregor at gmail.com> wrote:

>I installed Ubuntu Server 10.04.2 LTS AMD64 on a HP ProLiant ML370 G3 (4 x
>dual-core/hyperthreaded Xeon 2.66 GHz, 8 GB RAM) and I used the on-board
>SCSI controller to manage 8 x 300 GB 15K RPM SCSI drives in a software RAID
>5 set up as a 7-drive array with 1 hot-spare drive. All drives are the exact
>same model with the same firmware version.
>It's currently rebuilding the array (because I just created the array) and
>/proc/mdstat is reporting "finish=165.7min speed=25856K/sec". Does that
>sound "right" in the sense that it's the right order of magnitude? I though
>it should be higher, but I haven't set up such an array before, so I don't
>have anything to compare it to.
>If it's slow, does anyone have a suggestion for speeding it up?
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>Roundtable at muug.mb.ca

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