AWFUL reshape speed with raid5.

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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.

No meaningful change if I start with 3 disks and grow to 4, with or
without bitmap.

-- 
Jon
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