[linux-lvm] Usable space in PV
timofey at koolin.ru
Thu Oct 1 16:10:34 UTC 2015
Task - problem.
I make universal extender of filesystem (for example extend fs in
virtual computer after resize disk or add space to filesystem in hosting
server, etc.). Before extend volume group and filesystem I want to make
plan of extends. For plan I need to know how many bytes it can add to VG
from disk/partition. I know size of disk, partition, free space - and I
have to know free space after create PV on free space of disk.
I don't know how many LV will be on target system (system, which run
fsextender), I don't know fragmentation of it and etc.
Is any way to know how many space take metadata and how many space will
On 01.10.2015 14:26, Zdenek Kabelac wrote:
> Dne 30.9.2015 v 17:28 Timofey Koolin napsal(a):
>> Task: calc usable space of PV before create PV and before create
>> partition for
>> In my experiments usable space in PV = PVSize / ExtentSize *
>> ExtentSize with
>> integer operations.
>> But when Metadata may be large - when LVM have a lot of logical
>> volumes and it
>> can take more space.
>> I found in /etc/lvm/lvm.conf parameter pvmetadatasize = 255 secotors
>> What will if metadata will grow to more then 255 sectors?
> If you plan to host lots of LVs within a single VG (in range of hundreds)
> use i.e. 'pvcreate --metadatasize 5M'
> (i.e. ~7000 linear single segment LVs takes around 2.2MB and you need
> space for at least 2 metadatas to fit in)
> What I'm not quite sure is your 'task' - what's the purpose ?
> Do you want to do some 'sector' precise emulation of what lvm2 is
> doing by watching resuls of couple command with just subset of it's
> options ?
> Isn't better to read man pages ?
> linux-lvm mailing list
> linux-lvm at redhat.com
> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
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