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Old 08-06-2008, 01:31 AM   #1
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Registered: Jun 2006
Location: Brisbane, Australia
Distribution: Ubuntu 8.04
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How can I speed up a RAID 5 grow operation?

Hello all,

I am growing my RAID array again.

It consists of 4x500GB in RAID 5, growing to 5x500GB in RAID 5.

Unfortunately, at its current rate, it is going to take forever:

damien@mediabox:~$ cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md0 : active raid5 sda1[4] sdc1[0] sdd1[3] sde1[2] sdb1[1]
      1465151808 blocks super 0.91 level 5, 64k chunk, algorithm 2 [5/5] [UUUUU]
      [>....................]  reshape =  0.4% (2039168/488383936) finish=7388.0min speed=1094K/sec

unused devices: <none>
That is, assuming it stays at 1100KB/s, then it will about about 21 days to complete.

Given that I'd rather not wait that long, is there any way to speed it up?

I have seen fleeting references to:
damien@mediabox:~$ cat /proc/sys/dev/raid/speed_limit_min
damien@mediabox:~$ cat /proc/sys/dev/raid/speed_limit_max
But I have no idea what numbers should go in there, or even what the limits mean.

Old 08-06-2008, 07:02 PM   #2
Registered: Sep 2007
Location: SF Bay Area, CA
Distribution: CentOS, SLES 10+, RHEL 3+, Debian Sarge
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Those numbers mean what they say, in kilobytes per second. As far as your array is concerned, it also depends on your drive speed, controller, and peripheral bus used.

Upping the max value won't do anything, as your system will never reach that value unless you got some 4G FC attached DA or SAN storage on 4x or above PCI-E, which doesn't seem to be the case.

Instead, up the minimum. Try the following value:

echo 50000 > /proc/sys/dev/raid/speed_limit_min
YMMV...this may not work on some older kernels.

Last edited by kenoshi; 08-06-2008 at 07:04 PM.


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