[linux-lvm] Bad disk removal

[linux-lvm] Bad disk removal

[Barnaby Claydon]

Hey all,

So after lots of scans and log review, turns out 1 of the 8 IDE disks in 
my LVM is bad. (I know, IDE, yeahyeah...)

I currently have the affected volume group online, and it's mounted in 
XFS readonly,norecovery mode. XFS can't attempt repair because one of 
the bad sectors is the superblock so xfs_repair bombs.

Unfortunately I don't have 1.2TB of free space available to try and pull 
all the data off the VG before rebuilding it and replacing the failed 
drive. If I get a replacement for the bad drive and extend the VG, my 
question would be:

How fault tolerant is pvmove if it encounters unreadable/bad sectors on 
a disk? Will I hose the entire VG if pvmove bombs? Will pvmove skip the 
bad sectors after a few attempts and move on? Will pvmove refuse to even 
try?

I'm sure someone's had experience with this before. :) (Obviously I 
don't have RAID underneath the LVM, otherwise I'm sure this would be 
moot... lesson learned.)

Thanks all,
-Barnaby

Re: [linux-lvm] Bad disk removal

[Fredrik Tolf]

On Wed, 2006-04-05 at 14:41 -0400, Barnaby Claydon wrote:
> Hey all,
> 
> So after lots of scans and log review, turns out 1 of the 8 IDE disks in 
> my LVM is bad. (I know, IDE, yeahyeah...)

When this happened to me, I got a replacement drive as large as that
drive, and used dd to copy the PV data bit-by-bit to the new disk, and
then zeroed the sectors corresponding to the old bad sectors. It worked
fairly well, but the bad sectors were probably only file data blocks for
me.

As far as I managed to find out, pvmove will not handle bad sectors at
all, and abort when it finds any. It would be great if anyone could
correct me on that, though...

Fredrik Tolf

Re: [linux-lvm] Bad disk removal

[Jonathan E Brassow]

On Apr 5, 2006, at 10:51 PM, Fredrik Tolf wrote:

> On Wed, 2006-04-05 at 14:41 -0400, Barnaby Claydon wrote:
>> Hey all,
>>
>> So after lots of scans and log review, turns out 1 of the 8 IDE disks 
>> in
>> my LVM is bad. (I know, IDE, yeahyeah...)
>
> When this happened to me, I got a replacement drive as large as that
> drive, and used dd to copy the PV data bit-by-bit to the new disk, and
> then zeroed the sectors corresponding to the old bad sectors. It worked
> fairly well, but the bad sectors were probably only file data blocks 
> for
> me.
>
> As far as I managed to find out, pvmove will not handle bad sectors at
> all, and abort when it finds any. It would be great if anyone could
> correct me on that, though...
>

pvmove will ignore errors and copy as much as it can.  It will not 
retry failed sectors though.  pvmove basically mirrors the drives, so 
you can use the volume while the device is being copied.  When the copy 
is complete, pvmove breaks the mirror and leaves you with the LV 
remapped to the new device.

  brassow

Re: [linux-lvm] Bad disk removal

[Fredrik Tolf]

On Thu, 2006-04-06 at 09:45 -0500, Jonathan E Brassow wrote:
> pvmove will ignore errors and copy as much as it can.  It will not 
> retry failed sectors though.  pvmove basically mirrors the drives, so 
> you can use the volume while the device is being copied.  When the copy 
> is complete, pvmove breaks the mirror and leaves you with the LV 
> remapped to the new device.

Really? I was sure the manpage said otherwise, but now that I look
again, it doesn't seem to be saying anything at all about it. Should it
not be amended to explain this?

By the way, what happens to the sectors on the new disk that corresponds
to the bad ones on the old disk, and would that affect only that sector
on the new disk, or the entire containing PE?

Fredrik Tolf