Re: mdadm and fsck

[Andrew McGlashan <andrew.mcglashan@affinityvision.com.au>]

Hi Joey,

Joey L wrote:
> Thanks for the scripts and the reply !! now i think i understand raid on 
> linux a lot better - but do have additional questions :)

Great.

> My /dev/md0 the root filesystem came back - Thank God !! and you :)
> Info you requested :
> root@rider:~# mdadm --detail /dev/md0
> /dev/md0:
>         Version : 1.2
>   Creation Time : Mon Jun 27 08:51:23 2011
>      Raid Level : raid1
>      Array Size : 972654456 (927.60 GiB 996.00 GB)
>   Used Dev Size : 972654456 (927.60 GiB 996.00 GB)
>    Raid Devices : 2
>   Total Devices : 2
>     Persistence : Superblock is persistent
>
>     Update Time : Sat Sep 17 22:53:59 2011
>           State : clean
>  Active Devices : 2
> Working Devices : 2
>  Failed Devices : 0
>   Spare Devices : 0
>
>            Name : debian:0
>            UUID : f696d568:1f4226e3:42f0a70a:68e284a7
>          Events : 295206
>
>     Number   Major   Minor   RaidDevice State
>        2       8        1        0      active sync   /dev/sda1
>        1       8       17        1      active sync   /dev/sdb1
> -- this looks fine !

Yes.

> But my issue is /dev/md1 -- i rebooted the machine - now it does not 
> come up at all and do not know which drive i think is okay - I see both 
> in fdisk -l  and they are okay.
>
> I get this:
>
> root@rider:~# mdadm --detail /dev/md1
> mdadm: cannot open /dev/md1: No such file or directory

Then the RAID isn't detected and assembled, not even degraded.

The fdisk tool should be run for each device, not the partitions, so in 
this case just /dev/sdc and /dev/sdd -- not /dev/sdc1 or /dev/sdd1

> root@rider:~# fdisk -l /dev/sdc
>
> Disk /dev/sdc: 1000.2 GB, 1000204886016 bytes
> 255 heads, 63 sectors/track, 121601 cylinders
> Units = cylinders of 16065 * 512 = 8225280 bytes
> Sector size (logical/physical): 512 bytes / 512 bytes
> I/O size (minimum/optimal): 512 bytes / 512 bytes
> Disk identifier: 0x000d27a0
>
>    Device Boot      Start         End      Blocks   Id  System
> /dev/sdc1               1      121601   976760001   fd  Linux raid 
> autodetect


> root@rider:~# fdisk -l /dev/sdd
>
> Disk /dev/sdd: 1000.2 GB, 1000204886016 bytes
> 255 heads, 63 sectors/track, 121601 cylinders
> Units = cylinders of 16065 * 512 = 8225280 bytes
> Sector size (logical/physical): 512 bytes / 512 bytes
> I/O size (minimum/optimal): 512 bytes / 512 bytes
> Disk identifier: 0x000d4cc8
>
>    Device Boot      Start         End      Blocks   Id  System
> /dev/sdd1               1      121601   976760001   fd  Linux raid 
> autodetect


> How do I determine which drive is the key drive or the one to add first 
> to /dev/md1

I would try the following to see if the file system can be mounted 
successfully.  If one errors and the other works fine and you can see 
your files okay, then that should help -- perhaps then, make a backup of 
the "good" drive, just in case.

mkdir /mnt/sdc1 /mnt/sdd1
mount -o ro -type ext4 /dev/sdc1 /mnt/sdc1
mount -o ro -type ext4 /dev/sdd1 /mnt/sdd1

Hope that gets you enough to work out what is going on.

--
Kind Regards
AndrewM

Andrew McGlashan
Broadband Solutions now including VoIP