[PVE-User] LVM question

[Dominik Csapak]

Hi,

On 4/9/21 19:19, Leandro Roggerone wrote:
> Hi guys , after install a new storage to my box , had to create lvm-thin.
> Im not very good with lvm , after reading some docs , and links like:
> https://forum.proxmox.com/threads/how-to-create-an-lvm-thinpool-and-vz-directory-on-the-same-disk.62901/
> 
> I got a working solution  but have also some questions about it.
> This is what I did:
> 
>   wipefs -a /dev/sdb
> 
> sgdisk -N 1 /dev/sdb
> 
> pvcreate --metadatasize 1024M -y -ff /dev/sdb1
> 
> vgcreate --metadatasize 1024M proxvg /dev/sdb1
> 
> lvcreate -l 100%FREE --poolmetadatasize 1024M --chunksize 256 -T -n
> proxthin proxvg
> 
> lvcreate -n proxvz -V 1.1T proxvg/proxthin
> 
> mkfs.ext4 /dev/proxvg/proxvz
> 
> mkdir /media/vz
> 
> echo '/dev/proxvg/proxvz /media/vz ext4 defaults,errors=remount-ro 0 2' >>
> /etc/fstab
> 
> mount -a
> 
> 
> And have following result:
> 
> 
> root at pve2:~# lvs
>    LV            VG     Attr       LSize    Pool     Origin Data%  Meta%
>   Move Log Cpy%Sync Convert
>    proxthin      proxvg twi-aotz--    1.63t                 22.03  6.34
> 
>    proxvz        proxvg Vwi-aotz--    1.10t proxthin        1.67
> root at pve2:~# lvdisplay
>    --- Logical volume ---
>    LV Name                proxthin
>    VG Name                proxvg
>    LV UUID                4cEIr9-3ZVQ-vsy1-q9ZX-GsaD-7oq0-pZixsX
>    LV Write Access        read/write
>    LV Creation host, time pve2, 2021-04-01 13:09:41 -0300
>    LV Pool metadata       proxthin_tmeta
>    LV Pool data           proxthin_tdata
>    LV Status              available
>    # open                 3
>    LV Size                1.63 TiB
>    Allocated pool data    22.03%
>    Allocated metadata     6.34%
>    Current LE             428451
>    Segments               1
>    Allocation             inherit
>    Read ahead sectors     auto
>    - currently set to     256
>    Block device           253:2
> 
>    --- Logical volume ---
>    LV Path                /dev/proxvg/proxvz
>    LV Name                proxvz
>    VG Name                proxvg
>    LV UUID                huzpPT-g0Gd-3Jwb-2ydz-InHh-73vN-Jnc5TR
>    LV Write Access        read/write
>    LV Creation host, time pve2, 2021-04-01 13:10:12 -0300
>    LV Pool name           proxthin
>    LV Status              available
>    # open                 1
>    LV Size                1.10 TiB
>    Mapped size            1.67%
>    Current LE             288359
>    Segments               1
>    Allocation             inherit
>    Read ahead sectors     auto
>    - currently set to     256
>    Block device           253:4
> 
> 
> Have following comments:
> 
> I can create VMs on proxthin partition so it is ok.
> 
> I can create backup on  proxvz partition so it is ok.

Looks OK imho.

> 
> What im concerned about is:
> 
> Physic storage space is about 1.8TG , how is it possible to create a 1.6
> and 1.1T volumnes inside ?

LVM Thin is 'thin-provisioned' it only uses space when it is really written.

> It can be a problem in the future ?

yes, if you do not monitor your real usage, if the thinpool runs full,
you can lose data.

> I was thinking about reduce proxthin partition to 600Gb aprox , so it make
> same sense 1.1T + 600G aprox 1.8 T
> But there is no LV Path on proxthin partition so I can unmount and the
> reduce.
> So ..
> What im missing here ? do I need to reduce proxthin partition ( I do need
> the 1.1T partition to backup).

the LV 'proxvz' is inside the thinpool 'proxthin' so as long as you
never allocate more that ~500GiB of vm/ct volumes, it should be fine.

alos, on allocation, the thinpool will print warnings if the allocated
lvs are bigger than the space available

hope this helps

> Hope to be clear about this guys.
> Any comment would be wellcome.
> Leandro.
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