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Is it possible to use free space of a partition mounted on / as volume group?

I mean creating VG on that free space, does it cause any problem?

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up vote 1 down vote accepted

If by mounted on / you mean, that the disk space is formatted with a file system, then no, you cannot.

An example

  • I have a disk of 500 gigs
  • I format it to contain /boot with 200 MB and / with 499.8 GB
  • I only use 10 gigs of disk space, so I have 489.8 GB free space

If that is the case, you cannot use the 489.8 GB as disk for your volume group.

However, if this is the case

  • I have a disk of 500 gigs
  • I format it to contain /boot with 200 MB and / with 100 GB, leaving me with 399.8 GB unused disk

Then I can use the 399.8 GB to create a PV in LVM and add that PV to a VG.

EDIT: Well, actually you could

I just came to think of something after I posted the answer. I was wondering if you could use loop interfaces with LVM. And it turns out you can. I am right now booting up a test box to play a little with that. I will edit this to be the results after I'm done.

EDIT: Actually - you can do it

This is basically how I did:

dd if=/dev/zero of=sflvm01.img bs=100 count=2M
dd if=/dev/zero of=sflvm02.img bs=100 count=2M

losetup /dev/loop0 sflvm01.img 
losetup /dev/loop1 sflvm02.img 

pvcreate /dev/loop0
pvcreate /dev/loop1

vgcreate test01 /dev/loop0 /dev/loop1
lvcreate -n loopdisk01 -L 300M test01
mkfs.xfs /dev/test01/loopdisk01
mkdir /mnt/428830 ; mount /dev/test01/loopdisk01 /mnt/428830

And I ended up with

                      296M   16M  281M   6% /mnt/428830

So, technically yes. You can do that. I would still advice you not to, though. I use LVM for all my disk.

I cannot set up the loop interfaces until my LVM has started - but when LVM starts, it cannot find the loop devices. So, I would have to do it manually at all times.

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Really Thanks for you answer and the time you spent. – Zim3r Sep 16 '12 at 10:23

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