Re: reconstruct raid superblock

[Carl Karsten <carl@personnelware.com>]

A degraded array is just missing the redundant data, not needed data, right?

I am pretty sure I need all 4 disks.

Is there any reason to 0 out the bytes I want replaced with good bytes?

On Wed, Dec 16, 2009 at 11:21 PM, Majed B. <majedb@gmail.com> wrote:
> If your other disks are sane and you are able to run a degraded array,  then
> you can remove grub using dd then re-add the disk to the array.
>
> To clear the first 1MB of the disk:
> dd if=/dev/zero of=/dev/sdx bs=1M count=1
> Replace sdx with the disk name that has grub.
>
> On Dec 17, 2009 6:53 AM, "Carl Karsten" <carl@personnelware.com> wrote:
>
> I took over a box that had 1 ide boot drive, 6 sata raid drives (4
> internal, 2 external.)  I believe the 2 externals were redundant, so
> could be removed.  so I did, and mkfs-ed them.  then I installed
> ubuntu to the ide, and installed grub to sda, which turns out to be
> the first sata.  which would be fine if the raid was on sda1, but it
> is on sda, and now the raid wont' assemble.  no surprise, and I do
> have a backup of the data spread across 5 external drives.  but before
> I  abandon the array, I am wondering if I can fix it by recreating
> mdadm's metatdata on sda, given I have sd[bcd] to work with.
>
> any suggestions?
>
> root@dhcp128:~# mdadm --examine /dev/sd[abcd]
> mdadm: No md superblock detected on /dev/sda.
> /dev/sdb:
>          Magic : a92b4efc
>        Version : 00.90.00
>           UUID : 8d0cf436:3fc2d2ef:93d71b24:b036cc6b
>  Creation Time : Wed Mar 25 21:04:08 2009
>     Raid Level : raid6
>  Used Dev Size : 1465137408 (1397.26 GiB 1500.30 GB)
>     Array Size : 5860549632 (5589.06 GiB 6001.20 GB)
>   Raid Devices : 6
>  Total Devices : 6
> Preferred Minor : 0
>
>    Update Time : Tue Mar 31 23:08:02 2009
>          State : clean
>  Active Devices : 5
> Working Devices : 6
>  Failed Devices : 1
>  Spare Devices : 1
>       Checksum : a4fbb93a - correct
>         Events : 8430
>
>     Chunk Size : 64K
>
>      Number   Major   Minor   RaidDevice State
> this     6       8       16        6      spare   /dev/sdb
>
>   0     0       8        0        0      active sync   /dev/sda
>   1     1       8       64        1      active sync   /dev/sde
>   2     2       8       32        2      active sync   /dev/sdc
>   3     3       8       48        3      active sync   /dev/sdd
>   4     4       0        0        4      faulty removed
>   5     5       8       80        5      active sync
>   6     6       8       16        6      spare   /dev/sdb
> /dev/sdc:
>          Magic : a92b4efc
>        Version : 00.90.00
>           UUID : 8d0cf436:3fc2d2ef:93d71b24:b036cc6b
>  Creation Time : Wed Mar 25 21:04:08 2009
>     Raid Level : raid6
>  Used Dev Size : 1465137408 (1397.26 GiB 1500.30 GB)
>     Array Size : 5860549632 (5589.06 GiB 6001.20 GB)
>   Raid Devices : 6
>  Total Devices : 4
> Preferred Minor : 0
>
>    Update Time : Sun Jul 12 11:31:47 2009
>          State : clean
>  Active Devices : 4
> Working Devices : 4
>  Failed Devices : 2
>  Spare Devices : 0
>       Checksum : a59452db - correct
>         Events : 580158
>
>     Chunk Size : 64K
>
>      Number   Major   Minor   RaidDevice State
> this     2       8       32        2      active sync   /dev/sdc
>
>   0     0       8        0        0      active sync   /dev/sda
>   1     1       0        0        1      faulty removed
>   2     2       8       32        2      active sync   /dev/sdc
>   3     3       8       48        3      active sync   /dev/sdd
>   4     4       0        0        4      faulty removed
>   5     5       8       96        5      active sync
> /dev/sdd:
>          Magic : a92b4efc
>        Version : 00.90.00
>           UUID : 8d0cf436:3fc2d2ef:93d71b24:b036cc6b
>  Creation Time : Wed Mar 25 21:04:08 2009
>     Raid Level : raid6
>  Used Dev Size : 1465137408 (1397.26 GiB 1500.30 GB)
>     Array Size : 5860549632 (5589.06 GiB 6001.20 GB)
>   Raid Devices : 6
>  Total Devices : 4
> Preferred Minor : 0
>
>    Update Time : Sun Jul 12 11:31:47 2009
>          State : clean
>  Active Devices : 4
> Working Devices : 4
>  Failed Devices : 2
>  Spare Devices : 0
>       Checksum : a59452ed - correct
>         Events : 580158
>
>     Chunk Size : 64K
>
>      Number   Major   Minor   RaidDevice State
> this     3       8       48        3      active sync   /dev/sdd
>
>   0     0       8        0        0      active sync   /dev/sda
>   1     1       0        0        1      faulty removed
>   2     2       8       32        2      active sync   /dev/sdc
>   3     3       8       48        3      active sync   /dev/sdd
>   4     4       0        0        4      faulty removed
>   5     5       8       96        5      active sync
>
> --
> Carl K
> --
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Carl K
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