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.
