[linux-lvm] Reserve space for specific thin logical volumes

[Gionatan Danti]

On 12/09/2017 14:03, Zdenek Kabelac wrote:> # lvs -a
>    LV              VG Attr       LSize  Pool Origin Data%  Meta%  Move 
> Log Cpy%Sync Convert
>    [lvol0_pmspare] vg ewi-------  2,00m
>    lvol1           vg Vwi-a-tz-- 20,00m pool        40,00
>    pool            vg twi-aotz-- 10,00m             80,00  1,95
>    [pool_tdata]    vg Twi-ao---- 10,00m
>    [pool_tmeta]    vg ewi-ao----  2,00m
> [root at linux export]# lvcreate -V10 vg/pool
>    Using default stripesize 64,00 KiB.
>    Reducing requested stripe size 64,00 KiB to maximum, physical extent 
> size 32,00 KiB.
>    Cannot create new thin volume, free space in thin pool vg/pool 
> reached threshold.
> 
> # lvcreate -s vg/lvol1
>    Using default stripesize 64,00 KiB.
>    Reducing requested stripe size 64,00 KiB to maximum, physical extent 
> size 32,00 KiB.
>    Cannot create new thin volume, free space in thin pool vg/pool 
> reached threshold.
> 
> # grep thin_pool_autoextend_threshold /etc/lvm/lvm.conf
>      # Configuration option activation/thin_pool_autoextend_threshold.
>      # thin_pool_autoextend_threshold = 70
>      thin_pool_autoextend_threshold = 70
> 
> So as you can see - lvm2 clearly prohibits you to create a new thinLV
> when you are above defined threshold.

Hi Zdenek,
this is very good news (for me at least). Thank you very much for 
pointing me that!

Anyway, I can not find the relative configuration variable in lvm.conf. 
I am on 2.02.166(2)-RHEL7, should I use a newer LVM version to set this 
threshold?

> To keep things single for a user - we have a single threshold value.
> 
> 
> So what else is missing ?

This is a very good step, indeed. However, multiple threshold (maybe 
attached/counted against the single thin volume, in a manner similar to 
how refreservation does for ZVOLs) would be even better (in my use case, 
at least).

> Unfortunatelly lvm2 nor dm  can be responsible for whole kernel logic and
> all user-land apps...

Again, I am *not* saying, nor asking, that.

I would simply like to use thinp without fearing that "forgotten" 
snapshot fill up the thin pool. I have shown how this can easily 
achieved with ZVOLs and careful use/setting of the refreservation value, 
without any upper layer knowledge and/or intra-layer communications.

> So you are already happy right  :) ?

Sure! :)
Thanks.

-- 
Danti Gionatan
Supporto Tecnico
Assyoma S.r.l. - www.assyoma.it
email: g.danti at assyoma.it - info at assyoma.it
GPG public key ID: FF5F32A8