[linux-lvm] is it right to specify '-l' with all the free PE in VG when creating a thin pool?

[linux-lvm] is it right to specify '-l' with all the free PE in VG when creating a thin pool?

[Eric Ren]

Hello,

I find that it will fail to create a thin pool with all the free PE in VG as follows:

# pvs
   PV         VG   Fmt  Attr PSize   PFree
   /dev/sdb        lvm2 ---  200.00g 200.00g
# vgcreate vgtest /dev/sdb
   Volume group "vgtest" successfully created
# pvdisplay
   --- Physical volume ---
   PV Name               /dev/sdb
   VG Name               vgtest
   PV Size               200.00 GiB / not usable 32.00 MiB
   Allocatable           yes
   PE Size               4.00 MiB
   Total PE              51192
   Free PE               51192
   Allocated PE          0
   PV UUID               JD74c2-R4zZ-cgs5-c5Ty-1abQ-cf7l-gdSxzz
# lvcreate -l 51192 --thinpool thinpool0 vgtest
   Volume group "vgtest" has insufficient free space (51167 extents): 51192 required.

while it works when specifying '-l' this way:

# lvcreate -l 100%FREE --thinpool thinpool0 vgtest
   Logical volume "thinpool0" created.

Is this something by design? or something may be wrong?
I can replicate this on both:

CentOS Linux release 7.3.1611 (Core)
lvm2-2.02.166-1.el7.x86_64

and
SUSE Linux Enterprise Server 12 SP2
lvm2-2.02.120-72.8.x86_64

Thanks,
Eric

Re: [linux-lvm] is it right to specify '-l' with all the free PE in VG when creating a thin pool?

[Zdenek Kabelac]

Dne 9.3.2017 v 12:12 Eric Ren napsal(a):
> Hello,
>
> I find that it will fail to create a thin pool with all the free PE in VG as
> follows:
>
> # pvs
>   PV         VG   Fmt  Attr PSize   PFree
>   /dev/sdb        lvm2 ---  200.00g 200.00g
> # vgcreate vgtest /dev/sdb
>   Volume group "vgtest" successfully created
> # pvdisplay
>   --- Physical volume ---
>   PV Name               /dev/sdb
>   VG Name               vgtest
>   PV Size               200.00 GiB / not usable 32.00 MiB
>   Allocatable           yes
>   PE Size               4.00 MiB
>   Total PE              51192
>   Free PE               51192
>   Allocated PE          0
>   PV UUID               JD74c2-R4zZ-cgs5-c5Ty-1abQ-cf7l-gdSxzz
> # lvcreate -l 51192 --thinpool thinpool0 vgtest
>   Volume group "vgtest" has insufficient free space (51167 extents): 51192
> required.
>
> while it works when specifying '-l' this way:
>
> # lvcreate -l 100%FREE --thinpool thinpool0 vgtest
>   Logical volume "thinpool0" created.
>
> Is this something by design? or something may be wrong?
> I can replicate this on both:

Hi

Yes this is by DESIGN

When you specify '-l|-L'  you specify size of 'dataLV'  (logical size)
But then you need some more space for 'metadata' LVs (_tmeta & _pmspare)

-l100%FREE figure this automagically and reduces size a bit to fit in metadata LV.


Some 'future' version of lvm2 may support something like '--physicalsize' 
which will be 'a total size used for every allocation made by command).


Regards

Zdenek

Re: [linux-lvm] is it right to specify '-l' with all the free PE in VG when creating a thin pool?

[Eric Ren]

On 03/09/2017 07:46 PM, Zdenek Kabelac wrote:
> [snip]
>>
>> while it works when specifying '-l' this way:
>>
>> # lvcreate -l 100%FREE --thinpool thinpool0 vgtest
>>   Logical volume "thinpool0" created.
>>
>> Is this something by design? or something may be wrong?
>> I can replicate this on both:
>
> Hi
>
> Yes this is by DESIGN
>
> When you specify '-l|-L'  you specify size of 'dataLV'  (logical size)
> But then you need some more space for 'metadata' LVs (_tmeta & _pmspare)
>
> -l100%FREE figure this automagically and reduces size a bit to fit in metadata LV.
>
>
> Some 'future' version of lvm2 may support something like '--physicalsize' which will be 'a 
> total size used for every allocation made by command).
Hi Zdenek,

Thanks a lot for your clarification!

Looks some changes to thin-pool feature make it behave differently since a certain version.
It worked on lvm2-2.02.98 (sles12) by specifying '-l' with all the free PE. Anyway, '-l 
100%FREE'
looks more reasonable in such case:)

Regards,
Eric
>
>
> Regards
>
> Zdenek
>
> _______________________________________________
> linux-lvm mailing list
> linux-lvm@redhat.com
> https://www.redhat.com/mailman/listinfo/linux-lvm
> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
>

Re: [linux-lvm] is it right to specify '-l' with all the free PE in VG when creating a thin pool?

[Zdenek Kabelac]

Dne 10.3.2017 v 02:39 Eric Ren napsal(a):
> On 03/09/2017 07:46 PM, Zdenek Kabelac wrote:
>> [snip]
>>>
>>> while it works when specifying '-l' this way:
>>>
>>> # lvcreate -l 100%FREE --thinpool thinpool0 vgtest
>>>   Logical volume "thinpool0" created.
>>>
>>> Is this something by design? or something may be wrong?
>>> I can replicate this on both:
>>
>> Hi
>>
>> Yes this is by DESIGN
>>
>> When you specify '-l|-L'  you specify size of 'dataLV'  (logical size)
>> But then you need some more space for 'metadata' LVs (_tmeta & _pmspare)
>>
>> -l100%FREE figure this automagically and reduces size a bit to fit in
>> metadata LV.
>>
>>
>> Some 'future' version of lvm2 may support something like '--physicalsize'
>> which will be 'a total size used for every allocation made by command).
> Hi Zdenek,
>
> Thanks a lot for your clarification!
>
> Looks some changes to thin-pool feature make it behave differently since a
> certain version.
> It worked on lvm2-2.02.98 (sles12) by specifying '-l' with all the free PE.
> Anyway, '-l 100%FREE'
> looks more reasonable in such case:)

Well I'm pretty much sure it has never ever had different logic for this 
allocation (yep it's been me doing this and there is also large regression 
test suite running behind all the time...))  - you could have get success only 
by having some 'spare room' on different PV.

But as already mentioned you are not the only one who would like to have
control over 'total allocated size' so there is already a BZ about this and 
something will be implemented - thought it's not as easy as it may sound...
(-l100%FREE is quite a cheating piece of code ;))

Regards

Zdenek