How to align Logical Volumes on contiguous Physical Extents?

I have originally created 2 Logical Volumes in a Volume Group. The 2 Logical Volumes occupy the whole Volume Group and are sat on contiguous Physical Extents.

However, after I have shrunk the first Logical Volume (LV_root), it becomes smaller and empty Physical Extents appear between the 2 Logical Volumes. Here is the output from the "pvdisplay" command :

$ sudo pvdisplay --maps

  --- Physical volume ---
  PV Name               /dev/sda5
  VG Name               VG_i5_2500
  PV Size               99.65 GiB / not usable 2.00 MiB
  Allocatable           yes 
  PE Size               4.00 MiB
  Total PE              25510
  Free PE               3025
  Allocated PE          22485
  PV UUID               3nRvBS-qq10-8XZZ-n3x9-gfHx-hrxN-AouB3q

  --- Physical Segments ---
  Physical extent 0 to 18431:
    Logical volume  /dev/VG_i5_2500/LV_root
    Logical extents 0 to 18431
  Physical extent 18432 to 21456:
    FREE
  Physical extent 21457 to 25509:
    Logical volume  /dev/VG_i5_2500/LV_swap
    Logical extents 0 to 4052

I want to know that is there a way to move LV_swap towards LV_root so that there is no empty Physical Extents between them (i.e. in general, how to move Logical Volumes within the same Volume Group in order to make more rooms for contiguous free Physical Extents.) ?

Moreover, is Contiguous free Physical Extents necessary when creating new Logical Volumes in a Volume Group ?

user1129812

Posted 2012-06-11T00:21:29.077

Reputation: 273

Answers

There isn't an lvmove command in standard LVM (though HP may have one in a custom version).

The way to do this would be to move the contents of the volume off somewhere else, then delete it and recreate it, then copy back.

As your volume is swap, then moving the contents isn't necessary. You can swapoff, delete the volume, then create a new swap volume and swapon.

However, a goal of LVM could be said to not have to bother with any of this. Contiguous physical extents are not necessary to create a volume, it will just get inserted into the gaps. The main time you'd get a performance penalty is if you had a file that crossed non-contiguous extents and so would require an extra seek when being read.

Paul

Posted 2012-06-11T00:21:29.077

Reputation: 52 173

1There seems do not have the "lvmove" command, just have a "pvmove" command. "pvmove" seems could move a particular Logical Volume, but it needs another Physical Volume for the move and the solution becomes relatively complicated. I am wondering whether there is a "gparted" like LVM tool that could move Logical Volume in an easy way. – user1129812 – 2012-06-11T00:55:23.123

@user1129812 Yes, this is what I am saying, lvmove does not exist in standard LVM. pvmove would help if you had another pv, then you could move it back afterwards, and it would be moved such that it closes the gap. There isn't a tool like gparted to do this, so you are left with the option in the answer (or variants of it) – Paul – 2012-06-11T01:55:59.647

Yes. I have mis-interpreted your wordings in some ways. If there is not a gparted like LVM tool, then using "pvmove" may be the current best solution. Thanks for your suggestion. – user1129812 – 2012-06-11T03:51:29.720

According to the pvmove man-page there is the possibility to move extents around on the same device:

If the source and destination are on the same disk, the anywhere allocation policy would be needed, like this:

pvmove --alloc anywhere /dev/sdb1:1000-1999 /dev/sdb1:0-999

Maybe overlapping regions are forbidden but then you could move your volume in 2 steps:

pvmove --alloc anywhere /dev/sda5:21457-24481 /dev/sda:18432-21456
pvmove --alloc anywhere /dev/sda5:24482-25509 /dev/sda:21457-22484

Sunday

Posted 2012-06-11T00:21:29.077

Reputation: 341