On Fri, 29 Jan 2010 23:23:34 +1100
Neil Brown <neilb@xxxxxxx> wrote:
> On Sun, 24 Jan 2010 19:49:31 -0800
> Michael Evans <mjevans1983@xxxxxxxxx> wrote:
>
> > mdX : active raid5 sdd1[8](S) sdb1[7](S) sdf8[0] sdl8[4] sdk2[5]
> > sdc1[6] sdj6[3] sdi8[1]
> > Y blocks super 1.1 level 5, 128k chunk, algorithm 2 [6/6] [UUUUUU]
> >
> > # mdadm --grow /dev/mdX --level=6 --raid-devices=8
> > --backup-file=/root/mdX.backupfile
> >
> > mdX : active raid6 sdd1[8] sdb1[7] sdf8[0] sdl8[4] sdk2[5] sdc1[6]
> > sdj6[3] sdi8[1]
> > Y blocks super 1.1 level 6, 128k chunk, algorithm 18 [8/9] [UUUUUU_U]
> > [>....................] reshape = 0.0% (33920/484971520)
> > finish=952.6min speed=8480K/sec
> >
> > !!! mdadm 3.1.1 I wanted an 8 device raid-6; Why do you show 9?
>
> That is weird isn't it. It is showing that 8 devices are in the array, of
> which 9 are working. That cannot be right.
> More worrying is that the second last device claim to not be present, which
> doesn't seem right.
The second last device being missing is actually correct. The '_' doesn't
actually mean "missing" but just "not completely in-sync".
When you converted from RAID5 to RAID6 it added the 7th device which clearly
was not in-sync.
Then converting to an 8-device array added the 8th device, but as the array
was not expecting any data to be on this device it is by definition
in-sync and so represented by "U".
The only problem is that it says "9" are in-sync where it should say "7"
are.
The following patch, which I have submitted upstream, fixes this.
Thanks again for the report.
NeilBrown
Author: NeilBrown <neilb@xxxxxxx>
Date: Tue Feb 9 12:31:47 2010 +1100
md: fix 'degraded' calculation when starting a reshape.
This code was written long ago when it was not possible to
reshape a degraded array. Now it is so the current level of
degraded-ness needs to be taken in to account. Also newly addded
devices should only reduce degradedness if they are deemed to be
in-sync.
In particular, if you convert a RAID5 to a RAID6, and increase the
number of devices at the same time, then the 5->6 conversion will
make the array degraded so the current code will produce a wrong
value for 'degraded' - "-1" to be precise.
If the reshape runs to completion end_reshape will calculate a correct
new value for 'degraded', but if a device fails during the reshape an
incorrect decision might be made based on the incorrect value of
"degraded".
This patch is suitable for 2.6.32-stable and if they are still open,
2.6.31-stable and 2.6.30-stable as well.
Cc: stable@xxxxxxxxxx
Reported-by: Michael Evans <mjevans1983@xxxxxxxxx>
Signed-off-by: NeilBrown <neilb@xxxxxxx>
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index e84204e..b5629c3 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -5464,11 +5464,11 @@ static int raid5_start_reshape(mddev_t *mddev)
!test_bit(Faulty, &rdev->flags)) {
if (raid5_add_disk(mddev, rdev) == 0) {
char nm[20];
- if (rdev->raid_disk >= conf->previous_raid_disks)
+ if (rdev->raid_disk >= conf->previous_raid_disks) {
set_bit(In_sync, &rdev->flags);
- else
+ added_devices++;
+ } else
rdev->recovery_offset = 0;
- added_devices++;
sprintf(nm, "rd%d", rdev->raid_disk);
if (sysfs_create_link(&mddev->kobj,
&rdev->kobj, nm))
@@ -5480,9 +5480,12 @@ static int raid5_start_reshape(mddev_t *mddev)
break;
}
+ /* When a reshape changes the number of devices, ->degraded
+ * is measured against the large of the pre and post number of
+ * devices.*/
if (mddev->delta_disks > 0) {
spin_lock_irqsave(&conf->device_lock, flags);
- mddev->degraded = (conf->raid_disks - conf->previous_raid_disks)
+ mddev->degraded += (conf->raid_disks - conf->previous_raid_disks)
- added_devices;
spin_unlock_irqrestore(&conf->device_lock, flags);
}
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