Re: faulty array member

[Neil Brown <neilb@suse.de>]

On Thu, 18 Nov 2010 18:08:46 +0100
Roberto Nunnari <roberto.nunnari@supsi.ch> wrote:

> Hello.
> 
> I have a linux file-server with to 1TB sata disks
> in software raid1.
> 
> as my drives are no longer in full health raid put
> one array member in faulty state.

More accurately: as one of your drives reported a write error, md/raid put it
in 'faulty' state'.

> 
> A bit about my environment:
> 
> # uname -rms
> Linux 2.6.9-89.0.18.ELsmp i686

Wow, that's old!!

> 
> # cat /etc/redhat-release
> CentOS release 4.8 (Final)
> 
> 
> # parted /dev/sda print
> Disk geometry for /dev/sda: 0.000-953869.710 megabytes
> Disk label type: msdos
> Minor    Start       End     Type      Filesystem  Flags
> 1          0.031    251.015  primary   ext3        boot
> 2        251.016  40248.786  primary   ext3        raid
> 3      40248.787  42296.132  primary   linux-swap
> 4      42296.133 953867.219  primary   ext3        raid
> 
> # parted /dev/sdb print
> Disk geometry for /dev/sdb: 0.000-953869.710 megabytes
> Disk label type: msdos
> Minor    Start       End     Type      Filesystem  Flags
> 1          0.031  39997.771  primary   ext3        boot, raid
> 2      39997.771  42045.117  primary   linux-swap
> 3      42045.117  42296.132  primary   ext3
> 4      42296.133 953867.219  primary   ext3        raid
> 
> 
> # cat /proc/mdstat
> Personalities : [raid1]
> md1 : active raid1 sdb4[1] sda4[0]
>        933448704 blocks [2/2] [UU]
> md0 : active raid1 sdb1[1] sda2[2](F)
>        40957568 blocks [2/1] [_U]
> unused devices: <none>
> 
> 
> Don't ask me why the two drives are not specular
> and md0 is mapped sdb1+sda2.. I have no idea.
> It was made so by anaconda using kickstart during install.
> 
> 
> So, I was using debugfs:
> # debugfs
> debugfs 1.35 (28-Feb-2004)
> debugfs:  open /dev/md0
> debugfs:  testb 1736947
> Block 1736947 marked in use
> debugfs:  icheck 1736947
> Block   Inode number
> 1736947 <block not found>
> debugfs:  icheck 1736947 10
> Block   Inode number
> 1736947 <block not found>
> 10      7
> 
> in an attempt to locate the bad disk blocks, and after that
> software raid put sda2 in faulty state.
> 
> 
> Now, as smartctl is telling me that there are errors spread
> on all partitions used in both raids, I would like to take
> a full backup of at least /dev/md1 (that's still healthy).
> 
> The question is:
> Is there a way and is it safe to put back /dev/sda2 into
> /dev/md0 so that I'm sure I can backup even the blocks
> that are unreadable on the first array member but probably
> are still readable on failed device?
> 

You should get 'ddrescue' and carefully read the documentation.

Then 'ddrescue' from the best device to a new device, making sure to keep the
log file.
Then 'ddrescue' from the second best device to the same new device using the
same log file.  This will only copy blocks that couldn't be read from the
first device.

NeilBrown



> Thank you for your time and help!
> 
> Best regards.
> Robi
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