Re: pvresize after pvcreate changes PV size: expected?

[Zdenek Kabelac <zdenek.kabelac@gmail.com>]

Dne 11. 01. 25 v 23:21 Tilman Vogel napsal(a):
> Hi!
> 
> I just encountered the following and do not understand it. The confusing part 
> is that when I run pvresize without size parameter directly after pvcreate, 
> the size still seems to change even though pvcreate of course also uses the 
> underlying device size just as pvresize should.
> 
> I am attaching the test.sh for your reference.
> 
> What am I missing?
> 

Hi

You are missing that the actual size of usable count of PV extents  is not 
changed by a single bit.

The surrounding accounting changes with the lvm2 metadata content size accounting.

For a user of a PV it's important there is 24 free extents of 4MiB each in 
this case and this gives a usable size for LVs.

Rest is either unused alignment space or space dedicated to PV header & lvm2 
metadata.  This space is accounted a  bit differently when you create a new PV
or you work with already existing PV with already existing lvm2 metadata area.
Yeah - it might be possibly 'addressed' better and PV could be readjusted 
after initial create - but it's not a bug - so it avoids 'extra' clutering
of PV header space when it's not really necessary  (as unlike lvm2 metadata, 
PV header space is not using any backups - so the less it's touched, the 
better....)

Regards

Zdenek


PS: for small PV sizes like in this case - using smaller  extent size  (i.e. 
256K, and reducing metadata size to i.e. 192K) may  'boost' usable  space for LVs.