Re: dirty chunks on bitmap not clearing (RAID1)

[NeilBrown <neilb@suse.de>]

On Mon, 29 Aug 2011 11:30:56 -0500 Chris Pearson <kermit4@gmail.com> wrote:

> I have the same problem.  3 chunks are always dirty.
> 
> I'm using 2.6.38-8-generic and mdadm - v3.1.4 - 31st August 2010
> 
> If that's not normal, then maybe what I've done differently is that I
> created the array, raid 1, with one live and one missing disk, then
> added the second one later after writing a lot of data.
> 
> Also, though probably not the cause, I continued writing data while it
> was syncing, and a couple times during the syncing, both drives
> stopped responding and I had to power off.
> 
> # cat /proc/mdstat
> Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5]
> [raid4] [raid10]
> md127 : active raid1 sdd1[0] sdc1[2]
>       1904568184 blocks super 1.2 [2/2] [UU]
>       bitmap: 3/15 pages [12KB], 65536KB chunk
> 
> unused devices: <none>
> 
> # mdadm -X /dev/sd[dc]1
>         Filename : /dev/sdc1
>            Magic : 6d746962
>          Version : 4
>             UUID : 43761dc5:4383cf0f:41ef2dab:43e6d74e
>           Events : 40013
>   Events Cleared : 40013
>            State : OK
>        Chunksize : 64 MB
>           Daemon : 5s flush period
>       Write Mode : Allow write behind, max 256
>        Sync Size : 1904568184 (1816.34 GiB 1950.28 GB)
>           Bitmap : 29062 bits (chunks), 3 dirty (0.0%)
>         Filename : /dev/sdd1
>            Magic : 6d746962
>          Version : 4
>             UUID : 43761dc5:4383cf0f:41ef2dab:43e6d74e
>           Events : 40013
>   Events Cleared : 40013
>            State : OK
>        Chunksize : 64 MB
>           Daemon : 5s flush period
>       Write Mode : Allow write behind, max 256
>        Sync Size : 1904568184 (1816.34 GiB 1950.28 GB)
>           Bitmap : 29062 bits (chunks), 3 dirty (0.0%)

I cannot see how this would be happening.  If any bits are set, then they
will be cleared after 5 seconds, and then 5 seconds later the block holding
the bits will be written out so that they will appear on disk to be cleared.

I assume that if you write to the array, the 'dirty' count increases, but
always goes back to three?

And if you stop the array and start it again, the '3' stays there?

If I sent you a patch to add some tracing information would you be able to
compile a new kernel with that patch applied and see what it says?

Thanks,

NeilBrown


> 
> 
> Quoting NeilBrown <neilb@suse.de>:
> 
> > On Thu, October 15, 2009 9:39 am, aristizb@ualberta.ca wrote:
> >> Hello,
> >>
> >> I have a RAID1 with 2 LVM disks and I am running into a strange
> >> situation where having the 2 disks connected to the array the bitmap
> >> never clears the dirty chunks.
> >
> > That shouldn't happen...
> > What versions of mdadm and the Linux kernel are you using?
> >
> > NeilBrown
> >
> >>
> >> I am assuming also that when a RAID1 is in write-through mode, the
> >> bitmap  indicates that all the data has made it to all the disks if
> >> there are no dirty chunks using mdadm --examine-bitmap.
> >>
> >> The output of cat /proc/mdstat is:
> >>
> >> md2060 : active raid1 dm-5[1] dm-6[0]
> >>        2252736 blocks [2/2] [UU]
> >>        bitmap: 1/275 pages [12KB], 4KB chunk, file: /tmp/md2060bm
> >>
> >>
> >> The output of mdadm --examine-bitmap /tmp/md2060bm is:
> >>
> >> Filename : md2060bm
> >>             Magic : 6d746962
> >>           Version : 4
> >>              UUID : ad5fb74c:bb1c654a:087b2595:8a5d04a9
> >>            Events : 12
> >>    Events Cleared : 12
> >>             State : OK
> >>         Chunksize : 4 KB
> >>            Daemon : 5s flush period
> >>        Write Mode : Normal
> >>         Sync Size : 2252736 (2.15 GiB 2.31 GB)
> >>            Bitmap : 563184 bits (chunks), 3 dirty (0.0%)
> >>
> >>
> >> Having the array under no IO, I waited 30 minutes but the dirty data
> >> never gets clear from the bitmap, so I presume  the disks are not in
> >> sync; but after I ran a block by block comparison of the two devices I
> >> found that they are equal.
> >>
> >> The superblocks and the external bitmap tell me that all the events
> >> are cleared, so I am confused on why the bitmap never goes to 0 dirty
> >> chunks.
> >>
> >> How can I tell if the disks are in sync?
> >>
> >>
> >> Thank you in advance for any help
> --
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