[linux-lvm] show free space _inside_ logical volume

[Lyn Rees]

If you mount the filesystem, 'df' will tell you how big it is, you can 
compare that to the output of lvdisplay.
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Mr Lyn Rees
Senior Engineer, UIG
Information Services Computing Centre
Cardiff University, 40-41 Park Place,
Cardiff. CF10 3BB.
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Contact numbers:
 (029) 2087 9188 (direct)
 (029) 2087 4875 (reception)
 (029) 2087 4285 (fax)
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Email: rees at cardiff.ac.uk
Web: www.cardiff.ac.uk



From:
Gabriel <jarod125 at gmail.com>
To:
linux-lvm at redhat.com
Date:
01/12/2009 00:46
Subject:
[linux-lvm] show free space _inside_ logical volume



Hi all,

I'm interested to know if it is possible to check the amount of free
space _inside_ a LV. I know that usually a LV is fully "occupied" by a
partition, but there is a (short) period when there is a gap between
the size of the partition and the size of the LV it resides on. That
happens _after_ doing a lvextend and _before_ doing the resize
(expand) of the filesystem.

First thing I thought of was lvdisplay. While I can see how many LEs
the LV has, I cannot see how many of them are in use by the filesystem
and how many are free (the way pvdisplay shows total/free/allocated
PEs).

It was suggested to me that I try some filesystem tools (resize2fs,
dumpe2fs, tune2fs etc.) that might show me the free space. resize2fs
does not have a 'dry-run' option that would have shown the new size
(in blocks) of the filesystem and I didn't find anything useful in
tune2fs' manual either.

dumpe2fs shows various information such as block count, free blocks
and block size, but I see no modifications when running this before
and after the lvextend command.

I also tried parted -l, but to no avail.

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