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Re: [linux-lvm] Drive gone bad, now what?



John Stoffel wrote:

Gert> We've setup a simple server machine with a bunch of harddisks of
Gert> 60 and 80 Gb.

John> Did you just concatentate or stripe the data across all the drives?

Butting in, I would assume (dangerous, I know) concatenation and non-striped since that is the default LVM mode when creating LVs. This is the exact same setup I have, BTW.

John> If you had just a simple concatenation of all the disks, then you are
John> toast.  How do you expect LVM to restore the missing 60gb if there's
John> no parity information or mirrored blocks?  It's impossible!

Yes, but he can restore the LV (sans the missing 60 gigs, of course) and access the rest of the archive. I believe that's what he's after.

Gert> For now we let the system rest until lvm2 matures and maybe the
Gert> tools will be there to rescue this set of disks

The tools are already here. I did the same thing a while back. But it ain't always easy. :-)

Go back to LVM1. Then, find another disk with the _exact same size_ as the deceased disk. Plug it in and pvcreate it (unless the old one had a LVM partition, in which case you fdisk and create a LVM partition on the new one):
# pvcreate -ff /dev/ide/host0/bus1/target0/lun0/disc


Restore your metadata to the new, empty disk, so LVM can restore the LV:
# vgcfgrestore -n YourVGName /dev/ide/host0/bus1/target0/lun0/disc
# vgscan
# vgchange -ay
# reiserfsck --rebuild-tree /dev/YourVGName
# mount /dev/YourVGName

There are a number of pitfalls along the way (not finding a disk of the same size is probably #1, but there is a way. If you can't find one, pvcreate a larger disk with -s. Use vgcfgrestore -ll to list the VG metadata stored in the backup, including the exact size of the dead PV.) but this is the basic layout. Heinz was kind enough to walk me through this when I had problems so now I feel like an expert. ;-)

Gert> LVM seemed an easy way to expand when needed..

It is. It's also the primary reason I use it instead of RAID. However, if there's money behind the archive (in my case, there isn't) you can go for a hardware RAID solution that offers the ability to grow the RAID. You will still need a bunch of same-size disks, but I could live with that, maybe you could too.

You can also combine RAID and LVM in various ways in an attempt to minimize the need for spare disks and maximize the size of useable space. Perhaps one RAID-5 array of one size disks and use LVM to concatenate it with another RAID-5 set of differently-sized disks. You can use NFS or Coda to glue two or more file servers together over the network if you run out of physical space in one of the machines.

John> You've basically hit upon the basic tradeoffs here, though you're
John> missing a performance issue, in that you should really try to keep
John> just one drive per IDE channel if at all possible from a performance
John> point of view.

If he's doing the same trade-offs I am, he values size over performance (which is 'good enough' for many uses even with shared IDE channels).

   / Rickard Olsson,IT-Konsult/
  / Telefon: +46 70 635 01 42/
 / http://www.webhackande.se/




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