On Wed, 2012-11-21 at 17:53 +0100, Sebastian Riemer wrote:

On 21.11.2012 17:17, Ross Boylan wrote:

quoted

After I failed and removed a partition, mdadm --examine seems to show
that partition is fine.

Perhaps related to this, I failed a partition and when I rebooted it
came up as the sole member of its RAID array.

Is this behavior expected?  Is there a way to make the failures more
convincing?

Yes, it is expected behavior. Without "mdadm --fail" you can't remove a
device from the array. If you stop the array with the failed device,
then the state is stored in the superblock.

I'm confused.  I did run mdadm --fail.  Are you saying that, in addition
to doing that, I also need to manipulate sysfs as you describe below?
Or were you assuming I didn't mdadm --fail?

Ross

There is a difference in the way mdadm does it and the sysfs method.
mdadm sends an ioctl to the kernel. With the sysfs command the faulty
state is stored immediately in the superblock.

# echo faulty > /sys/block/md0/md/dev-sdb1/state

If you reassemble that you'll get the message:
mdadm: device 0 in /dev/md0 has wrong state in superblock, but /dev/sdb1
seems ok

There is a limit of how many errors are allowed on the device (usually 20).

If you do the following additionally, your device won't be used for
assembly anymore.
# echo 20 > /sys/block/md0/md/dev-sdb1/errors

I guess this is related to: /sys/block/md0/md/max_read_errors.

quoted

The drive sdb in the following excerpt does appear to be experiencing
hardware problems.  However, the failed partition that became the md on
reboot was on a drive without any reported problems.

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