Software RAID 5 - a long story

Hello --

I'll try to keep this as brief as I can.

A while back I created an LVM array from 4 1TB Maxtor externals. This LVM
was to serve as a temporary data dump, while two of my internal HDs, were
RMA'd.

During the waiting period, one of the Maxtors failed, and I lost my data.
Having learned my lesson, I pulled the Maxtor for RMA, and resconstructed
the three remaining as a RAID5 array, then created an LVM volume with it.
Lovely.

When the failed Maxtor's replacement returned, I decided to grow the RAID5
array with it. Everything was going fine until one of the other Maxtors
decided to die on me as well. Needless to say I was unimpressed.

The newly-failed unit has been pulled and RMA'd , but I notice that whenever
the just-replaced unit falls asleep, it "falls off" the SCSI chain and
disappears.

Usually, I reboot and then re-assemble the array (this is only temporary
after all), but this time I decided to re-add the device after switching it
off then back on again. Its designation changed from /dev/sdn1
to /dev/sdq1. However, mdadm added it as a spare device, instead of
a "normal" raid component, and of course updated its superblock
accordingly.

Now, I can't start the array at all. mdadm --examine /dev/sdn1 gives:

/dev/sdn1:
Magic : a92b4efc
Version : 00.90.00
UUID : 37e70d06:2fd37f7b:2b41430b:610aafc7
Creation Time : Sun Aug 19 00:33:28 2007
Raid Level : raid5
Used Dev Size : 976767936 (931.52 GiB 1000.21 GB)
Array Size : 2930303808 (2794.56 GiB 3000.63 GB)
Raid Devices : 4
Total Devices : 4
Preferred Minor : 5

Update Time : Sun Nov 4 21:44:14 2007
State : clean
Active Devices : 2
Working Devices : 3
Failed Devices : 1
Spare Devices : 1
Checksum : 6575e3e1 - correct
Events : 0.705392

Layout : left-symmetric
Chunk Size : 32K

Number Major Minor RaidDevice State
this 4 65 1 4 spare

0 0 8 241 0 active sync /dev/sdp1
1 1 0 0 1 faulty removed
2 2 8 225 2 active sync /dev/sdo1
3 3 0 0 3 faulty removed
4 4 65 1 4 spare


"Total Devices" should be 3 not 4, since no spares were specified at
creation time. The drive contents have not been modified, so what I need to
do is change the major/minor number of the drive in the MD superblock. Is
this possible? The "real" major and minor numbers are:
/dev/sdn(8,208) /dev/sdn1(8,209)



All help gratefully received,

Rohan Beckles
rohan.beckles@virgin.net

Rohan Beckles wrote:

> Hello --
>
> I'll try to keep this as brief as I can.
>
> A while back I created an LVM array from 4 1TB Maxtor externals. This LVM
> was to serve as a temporary data dump, while two of my internal HDs, were
> RMA'd.
>
> During the waiting period, one of the Maxtors failed, and I lost my data.
> Having learned my lesson, I pulled the Maxtor for RMA, and resconstructed
> the three remaining as a RAID5 array, then created an LVM volume with it.
> Lovely.
>
> When the failed Maxtor's replacement returned, I decided to grow the RAID5
> array with it. Everything was going fine until one of the other Maxtors
> decided to die on me as well. Needless to say I was unimpressed.
>
> The newly-failed unit has been pulled and RMA'd , but I notice that
> whenever the just-replaced unit falls asleep, it "falls off" the SCSI
> chain and disappears.
>
> Usually, I reboot and then re-assemble the array (this is only temporary
> after all), but this time I decided to re-add the device after switching
> it off then back on again. Its designation changed from /dev/sdn1
> to /dev/sdq1. However, mdadm added it as a spare device, instead of
> a "normal" raid component, and of course updated its superblock
> accordingly.
>
> Now, I can't start the array at all. mdadm --examine /dev/sdn1 gives:
>
> /dev/sdn1:
> Magic : a92b4efc
> Version : 00.90.00
> UUID : 37e70d06:2fd37f7b:2b41430b:610aafc7
> Creation Time : Sun Aug 19 00:33:28 2007
> Raid Level : raid5
> Used Dev Size : 976767936 (931.52 GiB 1000.21 GB)
> Array Size : 2930303808 (2794.56 GiB 3000.63 GB)
> Raid Devices : 4
> Total Devices : 4
> Preferred Minor : 5
>
> Update Time : Sun Nov 4 21:44:14 2007
> State : clean
> Active Devices : 2
> Working Devices : 3
> Failed Devices : 1
> Spare Devices : 1
> Checksum : 6575e3e1 - correct
> Events : 0.705392
>
> Layout : left-symmetric
> Chunk Size : 32K
>
> Number Major Minor RaidDevice State
> this 4 65 1 4 spare
>
> 0 0 8 241 0 active sync /dev/sdp1
> 1 1 0 0 1 faulty removed
> 2 2 8 225 2 active sync /dev/sdo1
> 3 3 0 0 3 faulty removed
> 4 4 65 1 4 spare
>
>
> "Total Devices" should be 3 not 4, since no spares were specified at
> creation time. The drive contents have not been modified, so what I need
> to do is change the major/minor number of the drive in the MD superblock.
> Is this possible? The "real" major and minor numbers are:
> /dev/sdn(8,208) /dev/sdn1(8,209)
>
>
>
> All help gratefully received,
>
I think, if you created a lvm, you'd want to examine the lvm uuid of the
drive as well (and set it again, according to
the /etc/lvm/backup/<volume_group> file)?
Btw., which checksum should the partition have according to mdadm.conf?

--
vista policy violation: Microsoft optical mouse found penguin patterns
on mousepad. Partition scan in progress to remove offending
incompatible products. Reactivate MS software.
Linux 2.6.17mm,Xorg7.2/nvidia [LinuxCounter#295241,ICQ#4918962]