[ClusterLabs] Note: Replacing disk of MD-RAID in SLES11SP4

[Ulrich Windl]

Hi!

I'd like to drop a small note on "mdadm .. --replace .. --with .." (new command to replace a specific disk with a hot spare without loosing redundancy)
In SLES11SP4 that command doesn't work (always gives: "mdadm: Failed to request replacement for ..")

The relevant part of the strace suggests that the kernel does not have the required feature:
[...]
open("/sys/block/md20/md/dev-dm-12/state", O_WRONLY) = 5
write(5, "want_replacement", 16)        = -1 EINVAL (Invalid argument)
close(5)                                = 0
write(2, "mdadm: Failed to request replace"..., 52mdadm: Failed to request replacement for /dev/dm-12
) = 52
[...]

Maybe I should also remark that I had created a support call on this. It seems the problem won't be fixed; instead it's recommended not to use the command above (instead to this: first fail one disk, then remove it from the RAID, then add another disk).

The feature should work in openSUSE 13.2, however.

Regards,
Ulrich