On Mon, Jul 28, 2008 at 12:39 PM, Jon Nelson
<jnelson-linux-raid@xxxxxxxxxxx> wrote:
> I built a raid5 with 2 devices (and --assume-clean) using 2x 4GB
> partitions (not logical volumes).
> I then grew it to 3 devices.
> The reshape speed is really really slow.
>
> vmstat shows I/O like this:
>
> 0 0 212 25844 141160 497484 0 0 0 612 673 1284 0 6 93 0
> 0 0 212 25164 141160 497748 0 0 0 19 594 1253 1 4 95 0
> 0 0 212 25044 141160 498004 0 0 0 0 374 445 0 1 99 0
> 1 0 212 25220 141164 498000 0 0 0 23 506 1149 0 3 96 1
> 0 0 212 25500 141164 498004 0 0 0 3 546 1416 0 5 95 0
>
> The min/max is 1000/200000.
> What might be going on here?
>
> Kernel is 2.6.25.11 (openSUSE 11.0 x86-64 stock)
>
> /proc/mdstat for this entry:
>
> md99 : active raid5 sdd3[2] sdc3[1] sdb3[0]
> 3903744 blocks super 1.0 level 5, 64k chunk, algorithm 2 [3/3] [UUU]
> [=>...................] reshape = 8.2% (324224/3903744)
> finish=43.3min speed=1373K/sec
>
>
> This is on a set of devices capable of 70+ MB/s.
I found some time to give this another shot.
It's still true!
Here is how I built the array:
mdadm --create /dev/md99 --level=raid5 --raid-devices=2
--spare-devices=0 --assume-clean --metadata=1.0 --chunk=64 /dev/sdb3
/dev/sdc3
and then I added a drive:
mdadm --add /dev/md99 /dev/sdd3
and then I grew the array to 3 devices:
mdadm --grow /dev/md99 --raid-devices=3
This is what the relevant portion of /proc/mdstat looks like:
md99 : active raid5 sdd3[2] sdc3[1] sdb3[0]
3903744 blocks super 1.0 level 5, 64k chunk, algorithm 2 [3/3] [UUU]
[=>...................] reshape = 6.1% (241920/3903744)
finish=43.0min speed=1415K/sec
The 1000/200000 min/max defaults are being used.
If I bump up the min to, say, 30000, the rebuild speed does grow to
hover around 30000.
As Justin Piszcz said:
There once was a bug in an earlier kernel, in which the min_speed is
what the rebuild ran at if you had a specific chunk size, have you
tried to echo 30000 > to min_speed? Does it increase it to 30mb/s for
the rebuild?
Yes, apparently, it does. However, 'git log drivers/md' in the
linux-2.6 tree doesn't show anything obvious for me. Can somebody
point me to a specific commit, patch, etc... because as of 2.6.25.11
it's apparently still a problem (on an otherwise idle system, too).
>
> No meaningful change if I start with 3 disks and grow to 4, with or
> without bitmap.
>
> --
> Jon
>
--
Jon
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