Re: Partitions not recognized when auto-assembling array in initramfs

[Neil Brown <neilb@suse.de>]

On Mon, 27 Dec 2010 16:18:08 +0100 Laurent Pinchart
<laurent.pinchart@ideasonboard.com> wrote:

> Hi everybody,
> 
> I've been struggling with a software RAID issue for several days now. Before 
> sending the computer back to the vendor and asking for real RAID support, I'd 
> like to try my luck here.

By "real RAID" I assume you mean "proprietary closed-source raid that is sold
to you in an ROM" :-)

> 
> The system as an Intel Matrix Storage SATA controller and two 250GB disks on 
> which I want to use a RAID1.
> 
> I've been able to create the array properly from a Gentoo installation CD 
> (this might be a detail, but it might also influence homehost values, so I 
> thought I'd mention it) with the metadata stored in IMSM format.
> 
> Assembling the array automatically from the installation CD works.
> 
> livecd ~ # mdadm --assemble --scan
> mdadm: Container /dev/md/imsm0 has been assembled with 2 drives
> mdadm: Started /dev/md/vol0_0 with 2 devices
> 
> livecd ~ # cat /proc/mdstat 
> Personalities : [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] 
> md126 : active (auto-read-only) raid1 sda[1] sdb[0]
>       244195328 blocks super external:/md127/0 [2/2] [UU]
>       
> md127 : inactive sdb[1](S) sda[0](S)
>       4514 blocks super external:imsm
>        
> unused devices: <none>
> 
> livecd ~ # cat /proc/partitions 
> major minor  #blocks  name
> 
>    7        0      94664 loop0
>    8        0  244198584 sda
>    8       16  244198584 sdb
>    8       32     998400 sdc
>    8       33     998368 sdc1
>    9      126  244195328 md126
>  259        0    5242882 md126p1
>  259        1    5242884 md126p2
>  259        2  233709560 md126p3
> 
> So far, so good.
> 
> I've then created an mdadm.conf file with mdadm -E --scan
> 
> livecd ~ # mdadm -E --scan    
> ARRAY metadata=imsm UUID=480da1d0:8150f280:7dd8425d:bec99c46
> ARRAY /dev/md/vol0 container=480da1d0:8150f280:7dd8425d:bec99c46 member=0 
> UUID=17e28225:34f7c425:eb78aece:05c29a40
> 
> livecd ~ # mdadm --assemble --scan
> mdadm: Container /dev/md/imsm0 has been assembled with 2 drives
> mdadm: Started /dev/md/vol0 with 2 devices
> 
> livecd ~ # cat /proc/mdstat 
> Personalities : [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] 
> md126 : active (auto-read-only) raid1 sda[1] sdb[0]
>       244195328 blocks super external:/md127/0 [2/2] [UU]
>       
> md127 : inactive sdb[1](S) sda[0](S)
>       4514 blocks super external:imsm
>        
> unused devices: <none>
> 
> livecd ~ # cat /proc/partitions 
> major minor  #blocks  name
> 
>    7        0      94664 loop0
>    8        0  244198584 sda
>    8       16  244198584 sdb
>    8       32     998400 sdc
>    8       33     998368 sdc1
>    9      126  244195328 md126
>  259        0    5242882 md126p1
>  259        1    5242884 md126p2
>  259        2  233709560 md126p3
> 
> Still good so far. The /dev/md/vol0_0 device is now called /dev/md/vol0.
> 
> Copying the mdadm.conf file to initramfs and rebooting, the array is correctly 
> assemble with mdadm --assemble --scan
> 
> livecd ~ # mdadm --assemble --scan
> mdadm: Container /dev/md/imsm0 has been assembled with 2 drives
> mdadm: Started /dev/md/vol0 with 2 devices
> 
> livecd ~ # cat /proc/mdstat 
> Personalities : [raid1]
> md126 : active (read-only) raid1 sda[1] sdb[0]
>       244195328 blocks super external:/md127/0 [2/2] [UU]
>       
> md127 : inactive sdb[1](S) sda[0](S)
>       4514 blocks super external:imsm
>        
> unused devices: <none>
> 
> However, no partitions are detected.
> 
> livecd ~ # cat /proc/partitions 
> major minor  #blocks  name
> 
>    8        0  244198584 sda
>    8       16  244198584 sdb
>    8       32     998400 sdc
>    8       33     998368 sdc1
>    9      126  244195328 md126
> 
> If I remove the /etc/mdadm.conf file from the initramfs image, the volume is 
> detected as vol0_0 instead of vol0 and the partitions are correctly detected.
> 
> I don't understand what's going on there, and how I could fix it. Help would 
> be greatly appreciated.
> 

That is very strange....
It might help if you could provide the complete boot logs so I can see
everything that happened leading up to the partitions not being there.  It
would help me see if they were never created, or created then removed.

The command
   blockdev --rereadpt /dev/md/vol0
should re-detect the partitions for you, so you could try doing something
with that as a temporary fix.

mdadm does sometime remove partitions, but only on things that it is about to
include in an array, so it shouldn't ever remove the partitions
on /dev/md/vol0.

So something odd is happening, and more logs are needed to guess what.

NeilBrown