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Question: Is there a tool supporting de-fragmentation of LVM2 logical volumes ? (Making their extents into consistent sequences)

Preferably by defining desired order of extents (something like "partition A on beginning of disk, B after A, but X on the end of PV")

Of course there is a need of considering following cases:

  • VG consists one PV
  • VG consists many PV, but each LV sits on one PV
  • VG consists many PV, LVs have their extents across many PV

If partitions can be stripped or not, can be discussed.

Know-how: It's possible to move ranges of extents with pvmove , e.g. : pvmove --alloc anywhere /dev/sdb1:1000-1999 /dev/sdb1:0-999 .

Reason: Because moving many ranges manually with pvmove is purely repeatable thing (questionable if brainless or not), I was curious if there exists tool for automatizing/supporting this process. If not... maybe doing one by myself - do you think such tool would be useful for other people?

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It's possible that there's no tool because there's no use case that requires it. I'm curious, why do you want to defragment? Is there a disk technology where there's a benefit for a typical extent size (4MB)? – Gilles Aug 19 '12 at 22:42
Let's consider traditional HardDrive (not SSD) performance characteristics - beginning of disk offers better performance than end. That's most important factor, why you might like to have extents related to some partition to be placed on beginning. – Grzegorz Wierzowiecki Aug 20 '12 at 18:50
For that kind of control, the simple way is to partition the disk into several physical volumes. – Gilles Aug 20 '12 at 20:52
But on the other hand it makes more mess in config files and all setup less flexible. I believe that solutions like mentioned by @JimParis LVM2 defragmenter or pvmove do the job. – Grzegorz Wierzowiecki Aug 20 '12 at 22:36

1 Answer

up vote 3 down vote

I've used LVM2 defragmenter before. It is not the simplest or best written, but it does the trick.

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Looks interesting. I need to try it. – Grzegorz Wierzowiecki Aug 20 '12 at 22:35

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