Re: Problem with mdadm 2.6.7

[Doug Ledford <dledford@redhat.com>]

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On Sun, 2008-07-27 at 18:24 +0300, Thomas Backlund wrote:
> Doug Ledford skrev:
> > On Sun, 2008-07-27 at 17:26 +0300, Thomas Backlund wrote:
> >> Hi,
> >> (please cc me as I'm not subscribed)
> >>
> >> I have hit a bug with mdadm 2.6.7
> >>
> >> It rebuilds my raid5 array on every boot
> >> (raid0 and raid1 arrays are not affected)
> >>
> >> This didn't happend with 2.6.4
> >>
> >> kernels tested are 2.6.24.7 and 2.6.25.12
> >>
> >> Arch is x86_64
> >> Distro Mandriva 2008.1, but I've tested wich kernel.org kernels and 
> >> upstream mdadm 2.6.7 and have the same problem
> >>
> >> Now I could try to bisect it, but every raid5 rebuild takes 6-7 hours, 
> >> so I thought about asking for pointers before...
> >>
> >> Any ideas where to start looking ?
> > 
> > Are you using mkinitrd (or something similar) to start the arrays, or
> > are you using udev rules that call mdadm --incremental --run?  If it's
> > the later, then this is what you get when A) the array is started as
> > soon as there are enough devices to run in degraded mode and B)
> > something writes to the array before the last device gets added and C)
> > you don't have a bitmap to allow the array to keep track of what blocks
> > need resynced and therefore it resynces the entire drive.
> > 
> 
> I'm using udev.
> 
> but looking at the difference between 2.6.4 and 2.6.7:
> 
> diff -Nurp mdadm-2.6.4/etc/udev/rules.d/70-mdadm.rules 
> mdadm-2.6.7/etc/udev/rules.d/70-mdadm.rules
> --- mdadm-2.6.4/etc/udev/rules.d/70-mdadm.rules	2008-07-27 
> 13:14:10.000000000 +0300
> +++ mdadm-2.6.7/etc/udev/rules.d/70-mdadm.rules	2008-07-27 
> 13:11:13.000000000 +0300
> @@ -3,4 +3,4 @@
>   # See udev(8) for syntax
> 
>   SUBSYSTEM=="block", ACTION=="add|change", 
> ENV{ID_FS_TYPE}=="linux_raid*", \
> -	RUN+="/sbin/mdadm --incremental $root/%k"
> +	RUN+="/sbin/mdadm --incremental --run --scan $root/%k"
> 
> 
> I see that --incremental was already there in 2.6.4, so I guess the 
> --run is the one messing with me...

Yep.  That'd be it.
> 
> 
> 
> as for --bitmap, can it be added to an existing array ?
> 
> What is the better choice, bitmap=internal or bitmap=<some_file> ?
> 
> I'd hate to have to recreate the array, as I have about 1.2GB of data on 
> it...

I use bitmap=internal on my arrays and never have a problem.

> --
> Thomas
-- 
Doug Ledford <dledford@redhat.com>
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              http://people.redhat.com/dledford

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