On Sat, Sep 14, 2013 at 12:38 PM, NeilBrown [off-list ref] wrote:

On Sat, 14 Sep 2013 00:35:47 +0200 Francis Moreau [off-list ref]
wrote:

quoted

Hi Neil,

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

quoted

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Finally I restart the array with the 2 disks (one disk is outdated)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the outdated disk first in that case: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

This isn't what I meant.
I mean that after you had run
  mdadm -I /dev/foo
for all devices, you then run
  mdadm -IRs
to start any that are degraded.

oh sorry I misunderstood what you previously wrote. Using '-I' to add
devices make mdadm to notice that one disk is outdated.

BTW I think I've fixed the issue with mdadm -R /dev/md125 for DDF.
Try the latest git.

It seems it fixes the issue: mdmon is now correctly started with a
degraded DDF array.

However, after using the system with only one disk (sda), sdb is now
outdated. I rebooted the system with 2 disks but mdadm doesn't seem to
notice that sdb is outdated:

# mdadm -I /dev/sda
mdadm: container /dev/md/ddf0 now has 1 device
mdadm: /dev/md/array1_0 assembled with 1 device but not started
# mdadm -I /dev/sdb
mdadm: container /dev/md/ddf0 now has 2 devices
mdadm: Started /dev/md/array1_0 with 2 devices (1 new)
# cat /proc/mdstat
Personalities : [raid1]
md126 : active (auto-read-only) raid1 sdb[1] sda[0]
      2064384 blocks super external:/md127/0 [2/2] [UU]

md127 : inactive sdb[1](S) sda[0](S)
      65536 blocks super external:ddf

So this time mdadm fails to kick out non fresh disk (when using '-I')
but with DDF.

Thanks
-- 
Francis