pvresize should defrag pv if necessary to reduce its size

[Eric Anopolsky]

The problem:
I have an LVM2 physical volume with a lot of free physical extents. But, when I try to shrink that physical volume with pvresize, it tells me that it can't. The reason is that there are allocated physical extents beyond the end of what would be the new physical volume.

The solution:
if( physicalExtentsBeyondEndOfRequestedPhysicalVolumeSize() ) {
    compactPhysicalExtentsToTheBeginningOfThePhysicalVolume();
}
shrinkPhysicalVolume();

This bug depends on bug #1. If that bug is fixed, I won't need to shrink LVM2 PVs.

[Paolo Sammicheli (xdatap1)]

Thank you for taking the time to report this bug and helping to make Ubuntu better. You reported this bug a while ago and there hasn't been any activity in it recently. We were wondering if this is still an issue for you. Can you try with the latest Ubuntu release? Thanks in advance.

[Paolo Sammicheli (xdatap1)]

We are closing this bug report because it lacks the information we need to investigate the problem, as described in the previous comments. Please reopen it if you can give us the missing information, and don't hesitate to submit bug reports in the future. To reopen the bug report you can click on the current status, under the Status column, and change the Status back to "New". Thanks again!

[Taylor Raack (track16)]

I'm reopening this, because I'm having the exact same problem as Paulo. I'm trying with Lucid 2.6.32-24-generic and LVM2 2.02.54-1ubuntu4. Is anyone willing to take a quick look at this and determine if it's something which can be fixed?

[Soren Hansen (soren)]

You should be able to use pvmove to move the offending physical extents within the pv. IIRC, the magic incantation is:

   pvmove -v /dev/whatever_your_pv_is_called

[Taylor Raack (track16)]

Soren, I just tried this out and sadly am having no luck. I run 'pvmove -v /dev/sdf1' (sdf1 is my pv) and the result I get is:

Finding volume group "mermaid"
  No extents available for allocation

But clearly I have extents on the pv, as reported by pvdisplay:
--- Physical volume ---
  PV Name /dev/sdf1
  VG Name mermaid
  PV Size 931.51 GiB / not usable 3.19 MiB
  Allocatable yes
  PE Size 4.00 MiB
  Total PE 238466
  Free PE 97497
  Allocated PE 140969
  PV UUID wGWKzs-Z1XJ-DFrd-jalf-0HOE-UM1x-V1GNZt

So, that doesn't seem to work. Does anything else come to mind?

[Taylor Raack (track16)]

I should have also mentioned that my vg only has one pv in it. Perhaps this is compounding the problem - there is no other pv in the group to which I can move extents. But really all I want to do is coalesce the extents on the existing pv so that I can physically shrink it.

[Soren Hansen (soren)]

And pvmove won't let you do that?
--
Sent from my Android phone with K-9 Mail. Please excuse my brevity.

[Phillip Susi (psusi)]

By default pvmove allocates extents on pvs OTHER than the one they are coming from. If you want to move extents around on the same PV, IIRC, you have to pass --alloc anywhere, and explicitly specify destination extents.

At any rate, this isn't really a bug. It is by design that you can not reduce a pv below its last allocated extent. If extent fragmentation is a problem, lvm currently does not support auto defragmentation. So this is really a feature request.