[PATCH] Do not assemble a duplicate of a running array

[Yury Polyanskiy]

On Thu, 14 Jul 2011 17:30:22 +1000
NeilBrown <neilb at suse.de> wrote:

> On Sun, 10 Jul 2011 21:08:53 -0400 Yury Polyanskiy <yp at mit.edu> wrote:
> 
> > Dear mdadm developers,
> > 
> > Consider the following scenario (based on a true story):
> 
> Hi,
>  thanks for the bug report and the patch.
> [...]
> 

Dear Neil,

I was wondering if you have anything new on this bug/patch?

Best,
Yury

> > SETUP:
> > * a raid1 MD array is configured with the name /dev/md/data (metadata=1.0).
> > * /dev/md/data is identified in the /etc/mdadm/mdadm.conf by its UUID
> > * /dev/md/data is assembled from the initramfs with minor /dev/md127
> > 
> > CRASH:
> > * [GLITCH] at some point one of the disks (/dev/sda) comprising /dev/md/data
> > experiences a bus-failure and is correctly removed from the array.
> > * array runs for some time in degraded state, data is being written and read
> > from the remaining disks (/dev/sdb, sdc etc)
> > * [REBOOT] after some time, the server is rebooted
> > * at boot time initramfs script starts /dev/md/data, but kernel correctly
> > kicks out /dev/sda from the array because the Event Counter is too old
> > ('kicking non-fresh sda from array').
> > * when udev starts, "mdadm --detail --export /dev/md127" correctly
> > identifies /dev/md127 and UDEV creates a correct symbolic link:
> >    /dev/md/data -> /dev/md127
> > 
> > * startup proceeds to execute /etc/init.d/mdadm-raid which runs "mdadm
> > --assemble --scan".
> > * mdadm --assemble --scan discovers the description of /dev/md/data in
> > mdadm.conf and finds a lonely /dev/sda with a matching UUID; /dev/md126 is
> > created out of a single /dev/sda
> > * now udev receives an ADD event for /sys/block/md126; again "mdadm --detail
> > --export /dev/md126" says that this device must be named /dev/md/data. UDEV
> > then re-creates the symbolic link, which now points to /dev/md126:
> >    /dev/md/data -> /dev/md126
> > 
> > * startup proceeds and /dev/md/data is mounted as a /home partition.
> > 
> > CONCLUSION:
> > * data written to /dev/md/data between GLITCH and REBOOT appears as lost now
> > (not mounted to /home).
> > * data written to /dev/md/data after REBOOT is stored on a buggy /dev/sda
> > instead of a sane array (/dev/sdb,/dev/sdc)
> > 
> > 
> > PATCH:
> > * attached is a patch against the master of http://neil.brown.name/git/mdadm
> > 
> > 
> > Best wishes,
> > Yury Polyanskiy
> 
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 198 bytes
Desc: not available
URL: <http://lists.alioth.debian.org/pipermail/pkg-mdadm-devel/attachments/20110824/0b5e03e0/attachment.pgp>