Hi Neil,

On Fri, Sep 13, 2013 at 10:43 PM, NeilBrown [off-list ref] wrote:

On Fri, 13 Sep 2013 15:22:20 +0200 Francis Moreau [off-list ref]
wrote:

quoted

Hi Neil,

I'm probably doing something wrong since it's a pretty critical bug
but can't see what.

I'm creating a RAID1 array with 1.2 metadata. After that I stop the
array, and restart the array with only one disk. I write random data
on the array and then stop it again:

# mkfs.ext4 /dev/md125
# mdadm --stop /dev/md125
# mdadm -IRs /dev/loop0
# mount /dev/md125 /mnt/
# date >/mnt/foo
# umount /mnt
# mdadm --stop /dev/md125

Finally I restart the array with the 2 disks (one disk is outdated)
and mdadm happily activates the array without error. Note that I add
the outdated disk first in that case:

# mdadm -IRs /dev/loop1
mdadm: /dev/loop1 attached to /dev/md/array1, which has been started.
# mdadm -IRs /dev/loop0
mdadm: /dev/loop0 attached to /dev/md/array1 which is already active.

That's a worry.  I'm not sure how to fix it.

I would probably suggest you don't use "-IR" to add devices.  That would make
it a lot less likely to happen.

Well I'm not sure how I should start an array...

For example doing:

# mdadm -I /dev/loop0
# mdadm -I /dev/loop1
# mdadm -R /dev/md125

works for array using metadata 1.2 but doesn't if the array is using
DDF (mdmon not started). To workaround this issue you suggested to use
-IRs:

# mdadm -IRs /dev/loop0
# mdadm -IRs /dev/loop1

but now mdadm can't detect outdated disk anymore.

Could you suggest something to start an array which would work in all
cases (ddf or 1.2, add non-fresh disk...) ?

quoted

# cat /proc/mdstat
Personalities : [raid1]
md125 : active raid1 loop0[0] loop1[1]
      117056 blocks super 1.2 [2/2] [UU]
# mount /dev/md125 /mnt
# ls /mnt/
[  457.321771] EXT4-fs error (device md125): ext4_lookup:1047: inode
#2: comm ls: deleted inode referenced: 12
ls: cannot access /mnt/1: Input/output error

If I add the outdated disk last I got this:
# mdadm -IRs /dev/loop0
mdadm: /dev/loop0 attached to /dev/md/array1, which has been started.
# mdadm -IRs /dev/loop1
mdadm: can only add /dev/loop1 to /dev/md/array1 as a spare, and
force-spare is not set.
mdadm: failed to add /dev/loop1 to existing array /dev/md/array1:
Invalid argument.

which didn't tell me the reason why loop1 must be a spare.

It  must be a spare because it is out of date.

Yes but I think mdadm should tell the reason, no  ?

Thanks
-- 
Francis