Frequently Asked Questions

Please add questions here.

  1. Do I need a special lvm2 kernel module?

  2. I get errors about /dev/mapper/control when I try to use the LVM 2 tools. What's going on?

  3. Is pvmove reasonably atomic? If the system goes down mid-pvmove, is my data hosed or do I just need to restart and try again?

  4. I think I found a bug. What information should I gather and how should I report it?

  5. Is there a way to activate/mount a copy of a volume group taken with a disk-array based point-in-time copy on the same host? The problem I have occurs because the disk-array copy contains all information on the disk, including PVID/VGID's, which is confusing for Linux's LVM.

  6. I am using LVM2 in a shared SAN environment, and would like to restrict access to a single server, and periodically switch the access of the volume groups from one host to another. Under vxvm, "vxdg <import/deport>" does this, and for LVM1, I could use the "System ID". Can I do this with LVM2?

  7. What does "Found duplicate PV bUO24Zb2mJGJrTSTRs87Lwrumlu72A1T: using /dev/loop2 not /dev/loop1" mean?

  8. How do I manage SAN based snapshots of LVM volumes?

Can I use pvmove on root volume ? What's special with it ?

Alternatively, to perform pvmove of root device you can

  1. Boot from different device (live cd) and perform move from here.

  2. If not possible: prepare environment and avoid some locking issues

  3. - obviously, backup data on the volume you are trying to move :-)

  4. - try to avoid moving swap (deactivate it)
  5. - use statically linked binaries lvm.static (and dmsetup.static) (use lvm.static pvmove <pars> instead of pvmove)

  6. - move these binaries to ramdisk or volume not included in root (moving) volume (keep in mind that shell runs from moving volume too !)
  7. - run pvmove
  8. - you can use pvmove --abort to abandon it or pvmove [or with same source pv as before] to retry.

    • If it fails (or gets stuck)
      • - if you reset machine, pvmove will restart automatically.
      • - (dangerous): you can wake up suspended device (which caused deadlock) by running dmsetup resume <suspended device>

  9. Note if you are trying to do some debugging: What you're looking for is anything that attempts to access the device being moved (e.g /dev /var /etc) while it's suspended - that process will block, and if it happens to be holding on to any resource that pvmove needs before unsuspending the device, things will lock up when pvmove tries to get that resource. It helps to get several backtraces from the deadlock situations - need to include *every* process - and look for things that they have in common. See if you can get it working in simpler environments first - e.g. disable locking in the config file; try with /etc, /dev, /var etc. in ram filesystems.

How can I debug problem myself ?

I see "reload ioctl failed", what's wrong ?

I cannot create more than X (usually 32) snapshots...

None: FrequentlyAskedQuestions (last edited 2009-02-05 16:57:11 by MilanBroz)