Re: Incorrect in-kernel bitmap on raid10

["Mario 'BitKoenig' Holbe" <Mario.Holbe@TU-Ilmenau.DE>]

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On Sun, Apr 19, 2009 at 04:24:02PM +1000, Neil Brown wrote:
> On Saturday April 18, Mario.Holbe@TU-Ilmenau.DE wrote:
> > I created a 4.5T RAID10 with internal bitmap out of 3 1.5T disks on a
> > and I get a strange inconsistency between the on-disk and the in-kernel
> > bitmap representation:
> Could you let me know if that following patch helps?

I attached the patch to 2.6.28 because of the still pending .29-fix.
It looks better but not perfect, if you ask me:

root@darkside:~# mdadm -G -b internal /dev/md7
[  137.605821] md7: bitmap file is out of date (0 < 8382) -- forcing full recovery
[  137.627777] md7: bitmap file is out of date, doing full recovery
[  137.871855] md7: bitmap initialized from disk: read 9/9 pages, set 268275 bits
[  137.893543] created bitmap (131 pages) for device md7
root@darkside:~# cat /proc/mdstat
Personalities : [raid1] [raid10]
md7 : active raid10 sdc1[0] sde1[4] sdd1[2]
      4395406848 blocks 512K chunks 2 near-copies [6/3] [U_U_U_]
      bitmap: 0/131 pages [0KB], 16384KB chunk
...

It looks like there are now enough pages allocated in-kernel.
So - yes, the patch helps :)

The "read 9/9 pages" message does still look somewhat strange but better
than before (where it was "read 1/1 pages, set 6131 bits") and it seems
to be similar to messages of my other raids.
The "set 268275 bits" message does not seem to be consistent to the
"bitmap: 0/131 pages [0KB]" mdstat, but this is quite likely unrelated
to the original problem.

root@darkside:~# mdadm -X /dev/sd[cde]1 | grep Bitmap
          Bitmap : 268275 bits (chunks), 137203 dirty (51.1%)
          Bitmap : 268275 bits (chunks), 137203 dirty (51.1%)
          Bitmap : 268275 bits (chunks), 137203 dirty (51.1%)

The discrepancy between the "0/131 pages [0KB]" in-kernel and the
"137203 dirty (51.1%)" on-disk seems to be another, unrelated issue.
I experienced somehow similar issues when adding a new component to an
existing bitmapped device. When the full-sync of the new component is
finished, the bitmap on the new component does usually show still lots
of dirty bits (sometimes only a few %, sometimes up to 95%) while the
other devices show 0 dirties. And this doesn't change over time or when
dropping page caches.


Mario
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