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Re: interesting MD-xfs bug

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: interesting MD-xfs bug
From: NeilBrown <neilb@xxxxxxx>
Date: Fri, 10 Apr 2015 09:36:52 +1000
Cc: Joe Landman <joe.landman@xxxxxxxxx>, linux-raid <linux-raid@xxxxxxxxxxxxxxx>, xfs <xfs@xxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20150409231035.GI13731@dastard>
References: <5526E8E9.3030805@xxxxxxxxx> <20150409221846.GG13731@dastard> <5526FB2A.8060704@xxxxxxxxx> <20150409225322.GH13731@dastard> <20150409231035.GI13731@dastard>
On Fri, 10 Apr 2015 09:10:35 +1000 Dave Chinner <david@xxxxxxxxxxxxx> wrote:

> On Fri, Apr 10, 2015 at 08:53:22AM +1000, Dave Chinner wrote:
> > On Thu, Apr 09, 2015 at 06:20:26PM -0400, Joe Landman wrote:
> > > 
> > > 
> > > On 04/09/2015 06:18 PM, Dave Chinner wrote:
> > > >On Thu, Apr 09, 2015 at 05:02:33PM -0400, Joe Landman wrote:
> > > >>If I build an MD raid0 with a non power of 2 chunk size, it appears
> > > >>that I can mkfs.xfs a file system, but it doesn't show up in blkid
> > > >>and is not mountable.  Yet, using a power of 2 chunk size, this does
> > > >>work correctly.   This is kernel 3.18.9.
> > > >>
> > > 
> > > [...]
> > > 
> > > >That looks more like a blkid or udev problem. try using blkid -p so
> > > >that it doesn't look up the cache but directly probes devices for
> > > >the signatures. strace might tell you a bit more, too. And if the
> > > >filesystem mounts, then it definitely isn't an XFS problem ;)
> > > 
> > > Thats the thing, it didn't mount, even when I used the device name
> > > directly.
> > 
> > Ok, that's interesting. Let me see if I can reproduce it locally. If
> > you don't hear otherwise, tracing would still be useful. Thanks for
> > the bug report, Joe.
> 
> No luck - md doesn't allow the device to be activated on 4.0-rc7:
> 
> $ sudo mdadm --version
> mdadm - v3.3.2 - 21st August 2014
> $ uname -a
> Linux test4 4.0.0-rc7-dgc+ #882 SMP Fri Apr 10 08:50:52 AEST 2015 x86_64 
> GNU/Linux
> $ sudo wipefs -a /dev/vd[ab]
> /dev/vda: 4 bytes were erased at offset 0x00001000 (linux_raid_member): fc 4e 
> 2b a9
> /dev/vdb: 4 bytes were erased at offset 0x00001000 (linux_raid_member): fc 4e 
> 2b a9
> $ sudo mdadm --create /dev/md20 --level=0 --metadata=1.2 --chunk=1152 
> --auto=yes --raid-disks=2 /dev/vd[ab]

Weird.  Works for me.
Any messages in 'dmesg' ??
How big are /dev/vd[ab]??

NeilBrown


> mdadm: RUN_ARRAY failed: Invalid argument
>        Problem may be that chunk size is not a power of 2
> $ cat /proc/mdstat
> Personalities : [raid1] [raid10] [raid6] [raid5] [raid4] 
> unused devices: <none>
> $
> 
> So I can't actually reproduce what you are seeing because MD doesn't
> allow the device to be activated and so mdadm tears it back down.
> 
> Cheers,
> 
> Dave.

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