RAID10 Resync fails with specific chunk size and drive sizes (reproducible)

[Peter Rabbitson]

Hi,

I think I've hit a reproducible bug in the raid 10 driver, tried on two 
different machines with kernels 2.6.20 and 2.6.18. This is a script to 
simulate the problem:

==
#!/bin/bash

modprobe loop

for ID in 1 2 3 ; do
echo -n Creating loopback device $ID... 
dd if=/dev/zero of=dsk${ID}.img bs=512 count=995967
losetup /dev/loop${ID} dsk${ID}.img
echo done.
done

mdadm -C /dev/md2 -l 10 -n 3 -p o2 -c 2048 /dev/loop1 /dev/loop2 /dev/loop3
echo Raid device assembled, check /proc/mdstat's output when resync is 
finished
==

This is the output I get in /proc/mdstat after the resync settles:

==
md2 : active raid10 loop3[2] loop2[3](F) loop1[0]
  746496 blocks 2048K chunks 2 offset-copies [3/2] [U_U]
==
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Re: RAID10 Resync fails with specific chunk size and drive sizes (reproducible)

[Peter Rabbitson]

After I sent the message I received the 6 patches from Neil Brown. I 
applied the first one (Fix Raid10 recovery problem) and it seems to be 
taking care of the issue I am describing. Probably due to the rounding 
fixes.

Thanks 

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