Re: [PATCH] md: Fix bug where new drives added to an md array sometimes don't sync properly.

[Eli Stair <estair@ilm.com>]

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Thanks Neil,

I just gave this patched module a shot on four systems.  So far, I 
haven't seen the device number inappropriately increment, though as per 
  a mail I sent a short while ago that seemed remedied by using the 1.2 
superblock, for some reason.  However, it appears to have introduced a 
new issue, and another is unresolved by it:



// BUG 1
The single-command syntax to fail and remove a drive is still failing, I 
do not know if this is somehow contributing to the further (new) issues 
below:

   [root@gtmp06 tmp]# mdadm /dev/md0 --fail /dev/dm-0 --remove /dev/dm-0
   mdadm: set /dev/dm-0 faulty in /dev/md0
   mdadm: hot remove failed for /dev/dm-0: Device or resource busy

   [root@gtmp06 tmp]# mdadm /dev/md0 --remove /dev/dm-0
   mdadm: hot removed /dev/dm-0


// BUG 2
Now, upon adding or re-adding a "fail...remove"'d drive, it is not used 
for resync.  I realized previously that added drives weren't re-synced 
until the existing array build was done, then they were grabbed.  This 
however is a clean/active array that is rejecting the drive.

I've performed this identically on both a clean & active array, as well 
as a newly-created (resync'ing) array, to the same effect.  Even after 
rebuild or reboot, the removed drive isn't taken back and remains listed 
as a "faulty spare", with dmesg indicating that it is "non-fresh".




// DMESG:

md: kicking non-fresh dm-0 from array!


// ARRAY status 'mdadm -D /dev/md0'

           State : active, degraded
  Active Devices : 13
Working Devices : 13
  Failed Devices : 1
   Spare Devices : 0

          Layout : near=1, offset=2
      Chunk Size : 512K

            Name : 0
            UUID : 05c2faf4:facfcad3:ba33b140:100f428a
          Events : 22

     Number   Major   Minor   RaidDevice State
        0     253        1        0      active sync   /dev/dm-1
        1     253        2        1      active sync   /dev/dm-2
        2     253        5        2      active sync   /dev/dm-5
        3     253        4        3      active sync   /dev/dm-4
        4     253        6        4      active sync   /dev/dm-6
        5     253        3        5      active sync   /dev/dm-3
        6     253       13        6      active sync   /dev/dm-13
        7       0        0        7      removed
        8     253        7        8      active sync   /dev/dm-7
        9     253        8        9      active sync   /dev/dm-8
       10     253        9       10      active sync   /dev/dm-9
       11     253       11       11      active sync   /dev/dm-11
       12     253       10       12      active sync   /dev/dm-10
       13     253       12       13      active sync   /dev/dm-12

        7     253        0        -      faulty spare   /dev/dm-0




Let me know what more I can do to help track this down.  I'm reverting 
this patch, since it is behaving less-well than before.  Will be happy 
to try others.

Attached are typescript of the drive remove/add sessions and all output.


/eli


Neil Brown wrote:
> On Friday October 6, estair@ilm.com wrote:
>  >
>  > This patch has resolved the immediate issue I was having on 2.6.18 with
>  > RAID10.  Previous to this change, after removing a device from the array
>  > (with mdadm --remove), physically pulling the device and
>  > changing/re-inserting, the "Number" of the new device would be
>  > incremented on top of the highest-present device in the array.  Now, it
>  > resumes its previous place.
>  >
>  > Does this look to be 'correct' output for a 14-drive array, which dev 8
>  > was failed/removed from then "add"'ed?  I'm trying to determine why the
>  > device doesn't get pulled back into the active configuration and
>  > re-synced.  Any comments?
> 
> Does this patch help?
> 
> 
> 
> Fix count of degraded drives in raid10.
> 
> 
> Signed-off-by: Neil Brown <neilb@suse.de>
> 
> ### Diffstat output
>  ./drivers/md/raid10.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff .prev/drivers/md/raid10.c ./drivers/md/raid10.c
> --- .prev/drivers/md/raid10.c   2006-10-09 14:18:00.000000000 +1000
> +++ ./drivers/md/raid10.c       2006-10-05 20:10:07.000000000 +1000
> @@ -2079,7 +2079,7 @@ static int run(mddev_t *mddev)
>                 disk = conf->mirrors + i;
> 
>                 if (!disk->rdev ||
> -                   !test_bit(In_sync, &rdev->flags)) {
> +                   !test_bit(In_sync, &disk->rdev->flags)) {
>                         disk->head_position = 0;
>                         mddev->degraded++;
>                 }
> 
> 
> NeilBrown
> 


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