Re: possible bug - bitmap dirty pages status

On Wed, Aug 31, 2011 at 4:56 PM, John Robinson
[off-list ref] wrote:

On 31/08/2011 13:30, Paul Clements wrote:

quoted

On Wed, Aug 31, 2011 at 5:05 AM, CoolCold[off-list ref]  wrote:

quoted

quoted

root@gamma2:~# cat /proc/mdstat
Personalities : [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md3 : active raid1 sdc3[1] sdb3[0]
     1443552640 blocks [2/2] [UU]
     bitmap: 16/22 pages [64KB], 32768KB chunk

quoted

More details now:
Array still has 16/22 dirty pages:

quoted

root@gamma2:~# mdadm --examine-bitmap /dev/sdc3

quoted

      Sync Size : 1443552640 (1376.68 GiB 1478.20 GB)
         Bitmap : 44054 bits (chunks), 189 dirty (0.4%)

But only 189 bits dirty. This means the bits are just distributed
across the disk (which is why you have 16/22 pages dirty).

Any activity on the disk? 189 bits could easily be explained by a
small amount of background disk activity on a disk that big.

That makes sense to me. I have:

$ cat /proc/mdstat
Personalities : [raid6] [raid5] [raid4] [raid1]
md1 : active raid6 sde2[4] sdd2[3] sdc2[2] sdb2[1] sda2[0]
     2929966080 blocks level 6, 512k chunk, algorithm 2 [5/5] [UUUUU]
     bitmap: 2/4 pages [8KB], 131072KB chunk

Oh no! Half my array is dirty! But then:

# mdadm --examine-bitmap /dev/sdb2
       Filename : /dev/sdb2
          Magic : 6d746962
        Version : 4
           UUID : d8c57a89:166ee722:23adec48:1574b5fc
         Events : 1338800
 Events Cleared : 1338800
          State : OK
      Chunksize : 128 MB
         Daemon : 5s flush period
     Write Mode : Normal
      Sync Size : 976655360 (931.41 GiB 1000.10 GB)
         Bitmap : 7452 bits (chunks), 7 dirty (0.1%)

Not so bad after all.

Makes sense, but...

On the other hand, repeatedly checking /proc/mdstat shows different numbers
of pages being dirty, and --examine-bitmap shows different numbers of bits
being dirty each time, whereas CoolCold managed 16 pages repeatedly and 189
bits being dirty twice in a row. CoolCold, please can you test
--examine-bitmap again several times at least 5 seconds apart?

fast test with "sleep 5" reveals:
root@gamma2:~# for i in {1..20};do mdadm --examine-bitmap
/dev/sdc3|grep "Bitmap :";sleep 5;done
          Bitmap : 44054 bits (chunks), 189 dirty (0.4%)
          Bitmap : 44054 bits (chunks), 189 dirty (0.4%)
          Bitmap : 44054 bits (chunks), 189 dirty (0.4%)
          Bitmap : 44054 bits (chunks), 189 dirty (0.4%)
          Bitmap : 44054 bits (chunks), 189 dirty (0.4%)
          Bitmap : 44054 bits (chunks), 189 dirty (0.4%)
          Bitmap : 44054 bits (chunks), 189 dirty (0.4%)
          Bitmap : 44054 bits (chunks), 189 dirty (0.4%)
          Bitmap : 44054 bits (chunks), 189 dirty (0.4%)
          Bitmap : 44054 bits (chunks), 189 dirty (0.4%)
          Bitmap : 44054 bits (chunks), 189 dirty (0.4%)
          Bitmap : 44054 bits (chunks), 189 dirty (0.4%)
          Bitmap : 44054 bits (chunks), 189 dirty (0.4%)
          Bitmap : 44054 bits (chunks), 189 dirty (0.4%)
          Bitmap : 44054 bits (chunks), 189 dirty (0.4%)
          Bitmap : 44054 bits (chunks), 189 dirty (0.4%)
          Bitmap : 44054 bits (chunks), 189 dirty (0.4%)
          Bitmap : 44054 bits (chunks), 189 dirty (0.4%)
          Bitmap : 44054 bits (chunks), 189 dirty (0.4%)
          Bitmap : 44054 bits (chunks), 189 dirty (0.4%)

And 16/22 lasts for 4 days.

Cheers,

John.

-- 
Best regards,
[COOLCOLD-RIPN]
--
To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html