11

I have three logical volumes in a single volume group using a single physical volume (the whole existing disk /dev/sda).

I now want to move one of those logical volumes to a new, faster disk, i.e., going from:

/dev/sda
    |-vg0-root → mounted to /
    |-vg0-foo  → mounted to /foo
    |-vg0-bar  → mounted to /bar

to:

/dev/sda
    |-vg0-root → mounted to /
    |-vg0-foo →  mounted to /foo

/dev/sdb
    |-vg1-bar  → mounted to /bar

From what I understand I cannot use pvmove or vgsplit because there's only one physical volume in the existing volume group.

What's a good approach to achieve this (preferably online, creating a new volume group for the new disk is not a requirement)?

  • I did check the many similar questions, but as far as I understand, those don't describe my situation. Bonus question: Is using a whole disk as physical volume a bad idea per se? It seems this decision made the solution much harder in my case. – htorque Mar 8 '15 at 9:15
  • 2
    Do you have any particular reason you don't want to add your new physical disk as a physical volume to the existing volume group? – Ulrich Schwarz Mar 8 '15 at 9:26
  • Not at all. If it makes things easier, the new disk can be part of vg0 as well. – htorque Mar 8 '15 at 9:31
16

One volume group solution:

 pvcreate /dev/sdb
 vgextend vg0 /dev/sdb
 pvmove -n /dev/vg0/bar /dev/sda /dev/sdb

Two volume group solution:

 pvcreate /dev/sdb
 vgcreate vg1 /dev/sdb
 lvcreate -l100%FREE vg1
 mkfs -t ext4 /dev/vg1/lvol1
 mount /dev/vg1/lvol1 /mnt

Now difficult part, all activities MUST stop on /bar:

 cd /mnt ; ( cd /bat ; tar cf - * ) | tar xf -
 cd /
 umount /mnt
 mount /dev/vg1/lvol1 /bar

where

  • pvcreate erase all data on disk (and prepare for LVM)
  • lvcreate sould create a logical volume lvol1, you specify lv name with -n bar
  • I use HP-UX syntax for lv, you might have to use /dev/mapper/myvg-mylv syntax

Once you have verified data are OK, in new place:

  • you can safely delete old /bar
  • edit /etc/fstab to use new /bar
  • Wow, seems I completely misread the pvmove man page. In that case I'll obviously settle for the one volume group solution. :) – htorque Mar 8 '15 at 9:52
  • Actually, one could use vgsplit after pvmove to achieve the two volume group solution a bit easier (however, the logical volume still needs to be deactivated using lvchange). – htorque Mar 8 '15 at 12:37
  • 1
    The usefulness of "pvmove" is a very good reason to use a single VG instead of multiple VGs. – tgharold Jul 5 '15 at 23:42
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    It seems like vgreduce can then be used to remove the old volume if that is the requirement (It wasn't for the specific question, but a question asking about moving all volumes would likely be marked a duplicate) – Gert van den Berg Nov 15 '16 at 13:43
  • My current experience is that in the single vg solution, pvmove requires an -n flag to specify the logical volume. Or it says a Physical volume /dev/vg0/bar not found Run `pvmove --help' for more information. error message. The man page says the same. May I insert it into the post? – user259412 Sep 11 '17 at 16:15

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