RE: raid6 - data integrity issue - data mis-compare on rebuilding RAID 6 - with 100 Mb resync speed.

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>On Wed, Apr 23, 2014 at 02:55:15PM +0530, Manibalan P wrote:
>> >On Fri, Apr 11, 2014 at 05:41:12PM +0530, Manibalan P wrote:
>> >> Hi Neil,
>> >> 
>> >> Also, I found the data corruption issue on RHEL 6.5.
>> >> 
>> 
>> >Did you file a bug about the corruption to redhat bugzilla?
>> 
>> Yes, today I raised a support ticket with Redhat regarding this issue.
>> 

>Ok, good. Can you paste the bz# ?

https://access.redhat.com/support/cases/01080080/

manibalan
 
>
>-- Pasi

> Manibalan
> 
> >-- Pasi
> 
> > For your kind attention, I up-ported the md code [raid5.c + raid5.h] 
> > from FC11 kernel to CentOS 6.4, and there is no mis-compare with the 
> > up-ported code.
> > 
> > Thanks,
> > Manibalan.
> > 
> > -----Original Message-----
> > From: Manibalan P
> > Sent: Monday, March 24, 2014 6:46 PM
> > To: 'linux-raid@xxxxxxxxxxxxxxx'
> > Cc: neilb@xxxxxxx
> > Subject: RE: raid6 - data integrity issue - data mis-compare on 
> > rebuilding RAID 6 - with 100 Mb resync speed.
> > 
> > Hi,
> > 
> > I have performed the following tests to narrow down the integrity issue.
> > 
> > 1. RAID 6, single drive failure - NO ISSUE
> > 	a. Running IO
> > 	b. mdadm set faulty and remove a drive
> > 	c. mdadm add the drive back
> >  There is no mis-compare happen in this path.
> > 
> > 2. RAID 6, two drive failure - write during Degrade and verify after 
> > rebuild
> > 	a. remove two drives, to make the RAID array degraded.
> > 	b. now run write IO write cycle, wait till the write cycle completes
> > 	c. insert the drives back one by one, and wait till the re-build 
> > completes and a RAID array become optimal.
> > 	d. now perform the verification cycle.
> > There is no mis-compare happened in this path also.
> > 
> > During All my test, the sync_Speed_max and min is set to 100Mb
> > 
> > So, as you referred in your previous mail, the corruption might be 
> > happening only during resync and IO happens in parallel.
> > 
> > Also, I tested with upstream 2.6.32 kernel from git:
> > "http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/ - 
> > tags/v2.6.32"
> > 	And I am facing mis-compare issue in this kernel as well.  on RAID 
> > 6, two drive failure with high sync_speed.
> > 
> > Thanks,
> > Manibalan.
> > 
> > -----Original Message-----
> > From: NeilBrown [mailto:neilb@xxxxxxx]
> > Sent: Thursday, March 13, 2014 11:49 AM
> > To: Manibalan P
> > Cc: linux-raid@xxxxxxxxxxxxxxx
> > Subject: Re: raid6 - data integrity issue - data mis-compare on 
> > rebuilding RAID 6 - with 100 Mb resync speed.
> > 
> > On Wed, 12 Mar 2014 13:09:28 +0530 "Manibalan P"
> > <pmanibalan@xxxxxxxxxxxxxx>
> > wrote:
> > 
> > > >
> > > >Was the array fully synced before you started the test?
> > > 
> > > Yes , IO is started, only after the re-sync is completed.
> > >  And to add more info,
> > >              I am facing this mis-compare only with high resync 
> > > speed (30M to 100M), I ran the same test with resync speed min 
> > > -10M and max
> > > - 30M, without any issue. So the  issue has relationship with 
> > > sync_speed_max / min.
> > 
> > So presumably it is an interaction between recovery and IO.  Maybe 
> > if we write to a stripe that is being recoverred, or recover a 
> > stripe that is being written to, then something gets confused.
> > 
> > I'll have a look to see what I can find.
> > 
> > Thanks,
> > NeilBrown
> > --
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