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Re: [linux-lvm] Question re: deleting an LV...

On 1/6/2014 7:59 AM, Tanstaafl wrote:
On 2013-12-30 8:03 AM, Tanstaafl <tanstaafl libertytrek org> wrote:

Due to a misunderstanding about how LVM snapshots work when I set up
this system, I now need to delete an LV I had created to use for this
purpose (I thought I had to pre-create the LV).

Currently I have:

  # lvscan
   ACTIVE            '/dev/vg/tmp' [5.00 GiB] inherit
   ACTIVE            '/dev/vg/log' [5.00 GiB] inherit
   ACTIVE            '/dev/vg/vtmp' [5.00 GiB] inherit
   ACTIVE            '/dev/vg/var' [700.00 GiB] inherit
   ACTIVE            '/dev/vg/snaps' [4.00 GiB] inherit

I just need to delete the /dev/vg/snaps LV, so that that 4GB is
available for my LVM snapshots.

Am I correct that all I have to do is:

# umount /dev/vg/snaps
# lvremove /dev/vg/snaps

Then remove this line from fstab?

This would then result in my VG having 4GB available for taking LVM

Would appreciate a confirmation that I don't have to do anything else to
totally eliminate the snaps LV...

I unmounted it, and commented that line in fstab. lvscan still shows the
same as above, but lvs shows the snaps with a slightly different attribute:

  # lvs
   LV    VG   Attr       LSize
   log   vg   -wi-ao----   5.00g
   snaps vg   -wi-a-----   4.00g
   tmp   vg   -wi-ao----   5.00g
   var   vg   -wi-ao---- 700.00g
   vtmp  vg   -wi-ao----   5.00g

So again - is lvremove /dev/vg/snaps the correct way - and the only
thing I need to do - to remove that LV as if it had never been created?

Yes. This page has a definition of the attributes: http://man7.org/linux/man-pages/man8/lvs.8.html. "o" in position 6 means device open; since you've unmounted it, it is no longer open.

I learned via this mailing list that lvremove just updates metadata to make the space available again, but doesn't remove the filesystem in the LV. So if you were to recreate the exact same LV you just removed, the filesystem would still be there. My situation was unusual, and you probably won't encounter this. But if you want to avoid that minor possibility, use "wipefs -a /dev/vg/snaps" before lvremove.

Guy Rouillier

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