[linux-lvm] Difference between Debian and some other distributions with thin provisioning

[Zdenek Kabelac]

Dne 29.9.2017 v 18:42 Jan Tulak napsal(a):
> Hi guys,
> I found out this difference and I'm not sure what is the cause. A
> command for creating a thin LV, which works on Archlinux, Centos and
> Fedora, fails on Debian and Ubuntu:
> 
> lvm lvcreate FOOvg1 \
>      -T \
>      -l 100%PVS \
>      -n FOOvg1_thin001 \
>      /dev/loop0 /dev/loop1 /dev/loop2

Hi

This command is not actually creating 'thin'  - only a thin-pool.
For 'thin' you need to specify -V  --virtualsize.

The usage of -T  is 'smart' flag - telling lvm2 to do 'something' 
thin/thin-pool oriented.

If you want to be 'exact' you can use --type thin  or --type thin-pool giving 
you more errors and requiring user more specific option for passing in.


> When it is created, lvs shows attributes "twi-a-tz--". But Debian and
> Ubuntu complain that  "--name may only be given when creating a new
> thin Logical volume or snapshot," even though the command states it
> should be thin with -T. A script that tests this issue is at the end
> of this email

Yep - the logic of command is internally enhanced over time and when user does 
specify parameters in a way where lvm2 can interpret them uniquely - it will 
do it.

BTW step-by around ;) for detailed explanation of all possible combination 
users can use to create  thin-pool or thin or both volumes at the same time.

> Do you know if there is a reason for this different behaviour?

It's not different -  newer version is 'enhanced' and just accepts wider 
syntax range.

> Versions seem to be close enough for it not to be a change in LVM

Hmm, close enough 111 and 171 ??


> behaviour, so I suspect some downstream or configuration changes. All
> tested distributions were run in their current stable versions, up to
> date. For example:

The original naming convention with pool names was to add the name next to VG 
name.

lvcreate -T -L10 vg/pool

Pool is 'special' type of LV - thus it got this privileged naming and standard 
option --name was normally left for  'thin' when user specifies -V.

Newer version of lvm2 can use  --name with --size specifier for pool name
when there is no virtual size given as its unique combination.

> Debian:
> # cat /etc/debian_version
> 8.9
> # lvm version
>    LVM version:     2.02.111(2) (2014-09-01)
>    Library version: 1.02.90 (2014-09-01) >    Driver version:  4.27.0

I'd suggest upgrading your Debian machine....

Regards

Zdenek