-----Original Message-----
From: NeilBrown [mailto:neilb@suse.de]
Sent: Wednesday, December 14, 2011 5:42 AM
To: Kwolek, Adam
Cc: linux-raid@vger.kernel.org
Subject: Re: Raid0 expansion problem in md

On Tue, 13 Dec 2011 15:45:30 +0000 "Kwolek, Adam"
[off-list ref]
wrote:

quoted

Hi Neil,

On the latest md neil_for-linus branch I've found raid0 migration problem.
During OLCE in user space everything goes fine, but in kernel process is not

moved forward.

quoted

/older md works fine/

It is stopped in md in reshape_request() in line (near raid5.c:3957)
    wait_event(conf->wait_for_overlap,
atomic_read(&conf->reshape_stripes)==0);

I've found that this problem is a side effect of patch:
    md/raid5: abort any pending parity operations when array fails.
and added line in this patch:
     sh->reconstruct_state = 0;

During OLCE we are going inside because condition
    if (s.failed > conf->max_degraded) with values:
     locked=1 uptodate=5 to_read=0 to_write=0 failed=2 failed_num=4,1

and sh->reconstruct_state is set to 0 (reconstruct_state_idle) from 6
(reconstruct_state_result) When sh->reconstruct_state is not reset raid0

migration is executed without problem.

quoted

Problem is probably in not executed code for finishing reconstruction
(around raid5.c:3300)

In our case field s.failed should not reach value 2 but we've got it for

failed_num = 4,1.

quoted

It seems that '1' is failed disk for stripe in old array geometry and 4 is failed

disk for stripe in new array geometry.

quoted

This means that degradation during reshape is counted two times /final

stripe degradation is sum of old and new geometry degradation/.

quoted

When we reading (from old array) and writing (to new geometry) a
degraded stripe  and degradation is on different positions (raid0 OLCE case)

analyse_stripe() gives us false failure information. Possible that we should
have old_failed and new_failed counters to know in what geometry
(old/new) failure occurs.

quoted

Here is reproduction script:

export IMSM_NO_PLATFORM=1
#create container
mdadm -C /dev/md/imsm0 -amd -e imsm -n 4 /dev/sdb /dev/sdc /dev/sde
/dev/sdd -R #create array mdadm -C /dev/md/raid0vol_0 -amd -l 0
--chunk 64 --size  1048 -n 1 /dev/sdb  -R --force #start reshape mdadm
--grow /dev/md/imsm0 --raid-devices 4


Please let me know your opinion.

Thanks for the excellent problem report.

I think it is best fixed by the following patch.
I also need to fixed up the calculate of 'degraded' so it doesn't say '2' in this
case, which is confusing.  Then I'll commit the fixes.


Thanks,
NeilBrown

Yes this helps :)
Thanks Neil,

BR
Adam