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

[Guy Rouillier <guy.rouillier@gmail.com>]

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