Today I was trying to reshape a RAID 5, going from 3 RAID disks to 4,
using the new mdadm 3.3 release. I had already added the new
partition to the array, which was marked as spare. Then I ran
`/sbin/mdadm -G -n4 /dev/md127` to start the reshape. Unfortunately,
it would always return "Failed to initiate reshape".
After a little digging, I found that this was because I'm running a
SUSE SLE11-SP3 kernel, which has partially-implemented support for
changing data_offset. In raid5.c:raid5_start_reshape(), I found this:
/* Don't support changing data_offset yet */
if (rdev->new_data_offset != rdev->data_offset)
return -EINVAL;
So, I understand where the "Failed to initiate reshape" error is
coming from. But is there perhaps a better way to handle this
situation? I also found that new_data_offset does not get restored
after hitting this error, so further attempts to reshape using a
backup-file continued to fail. Would it make sense to at least set
new_data_offset back to what it was when we fail to initiate the
reshape?
Thanks,
-Justin
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