Re: MD device always starting as /dev/md127

[NeilBrown <neilb@suse.de>]

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On Tue, 18 Sep 2012 19:19:53 -0400 Bryan Bush <bbushvt@gmail.com> wrote:

> I've moved the drives from one system to another and when the array
> starts up its always /dev/md127.
> /etc/mdadm/mdadm.conf has:
> 
> 
> # mdadm.conf
> #
> # Please refer to mdadm.conf(5) for information about this file.
> #
> 
> # by default (built-in), scan all partitions (/proc/partitions) and all
> # containers for MD superblocks. alternatively, specify devices to scan, using
> # wildcards if desired.
> DEVICE partitions containers
> 
> # auto-create devices with Debian standard permissions
> CREATE owner=root group=disk mode=0660 auto=yes
> 
> # automatically tag new arrays as belonging to the local system
> HOMEHOST <system>
> 
> # instruct the monitoring daemon where to send mail alerts
> MAILADDR root
> 
> # definitions of existing MD arrays
> ARRAY /dev/md1 level=raid6 metadata=1.2 num-devices=13
> UUID=fa32e2c5:e7bda20b:32af7c90:c7ee61eb
> 
> 
> mdadm --detail gives me
> 
> 
> 
> /dev/md127:
>         Version : 1.2
>   Creation Time : Sat Sep 18 17:05:52 2010
>      Raid Level : raid6
>      Array Size : 21488647488 (20493.17 GiB 22004.38 GB)
>   Used Dev Size : 1953513408 (1863.02 GiB 2000.40 GB)
>    Raid Devices : 13
>   Total Devices : 13
>     Persistence : Superblock is persistent
> 
>     Update Time : Tue Sep 18 17:40:47 2012
>           State : clean
>  Active Devices : 13
> Working Devices : 13
>  Failed Devices : 0
>   Spare Devices : 0
> 
>          Layout : left-symmetric
>      Chunk Size : 64K
> 
>            Name : 1
>            UUID : fa32e2c5:e7bda20b:32af7c90:c7ee61eb
>          Events : 56603
> 
>     Number   Major   Minor   RaidDevice State
>        0       8      177        0      active sync   /dev/sdl1
>       14       8      161        1      active sync   /dev/sdk1
>        2       8       81        2      active sync   /dev/sdf1
>        3       8      145        3      active sync   /dev/sdj1
>        4       8      209        4      active sync   /dev/sdn1
>        8       8       65        5      active sync   /dev/sde1
>        6       8       49        6      active sync   /dev/sdd1
>        7       8       33        7      active sync   /dev/sdc1
>       13       8      225        8      active sync   /dev/sdo1
>       15      65       17        9      active sync   /dev/sdr1
>       11      65        1       10      active sync   /dev/sdq1
>       10       8      241       11      active sync   /dev/sdp1
>        9       8      193       12      active sync   /dev/sdm1
> 
> 
> If I do
> mdadm --stop /dev/md127
> then
> mdadm --assemble --scan
> It starts the array at /dev/md1
> 
> Any idea why it always starts as md127?
>

My guess is that it is being started while the initrd is running, and the
initrd doesn't have that mdadm.conf.
So mdadm doesn't know what number to associated with the uuid, and so chooses
an unused one.

The metadata does say "Name : 1", but that isn't trusted unless there is some
reason to believe that the array belongs to "this" host.

If you:
  mdadm -S /dev/md127
  mdadm -A /dev/md1 --update=name /dev/sd[lkfjnedcorqpm]1
then it should update the metadata so that it is known to belong to "this"
host.  Then providing that the hostname is set during the initrd, it should
get the right name.
Or maybe arrange for the ARRAY entry to appear in the mdadm.conf in the
initrd.

NeilBrown


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