Re: [linux-lvm] size of lvm metadata

["Tomas Dalebjörk" <tomas.dalebjork@gmail.com>]

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Hi

if I have a disk that are merged into a server coming from another server containing a lvm snapshot
How can I convert this foreign disk to an existing  lv volume?

The documentation says I can use
lvconvert-Zn -s targetvg/targetlv sourcevg/sourcelv

But I guess I have to perform some lvm metadata recreation first?

please let me know what steps are neede

Regards Tomas

Sent from my iPhone

> On 17 Sep 2020, at 17:22, Heinz Mauelshagen <heinzm@redhat.com> wrote:
> 
>  Tomas,
> 
> the first PE starts at offset 2048 sectors of size 512 bytes by default, i.e. the LVM MDA (metadata area)
> is ~1MiB big (because the MDA starts at offset 1 page into the device).  If you plan for large numbers of LVs or expect very scattered allocations which both grow the metadata, you may want to create a
> bigger MDA using vgcreate's option --metadatasize (also see /etc/lvm/lvm.conf description on
> metadata/pvmetadatasize).
> 
> On 9/16/20 5:50 PM, Tomas Dalebjörk wrote:
> > hi
> > 
> > I am trying to understand how big the lvm metadata is
> > 
> > in the vgcfgbackup file, I can see extent_size = 8192 dev_size =
> > 204800 pe_start = 2048 pe_count 24
> > 
> > pe_count(24) * extent_size(8192) = 196608 bytes usable space of the
> > total dev_size(204800) metadata size? = dev_size(204800) - 196608 =
> > 8192
> > 
> > but... pe_start is 2048? so what is pe_start here? cant be
> > sectors(512)? bytes? well than ther be not aligned
> > 
> > so where starts the actual data? and where ends the lvm metadata?
> At offset 2048 sectors (1MiB into the device) / MDA ends at sector 2047.
> 
> Mind that lvm2 metadata is text formatted (see /etc/lvm/backup/$VGName for one)
> and thus varies in size (the MDA is used as a ring buffer for 2 copies of the MDA to
> support atomic updates).  As pointed out above when refering to 'vgcreate --metadatasize',
> in more elaborate setups you may run out of MDA space.
> 
> Heinz
> 
> > 
> > regards Tomas Sent from my iPhone
> > 
> > 
> > _______________________________________________ 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/
> 

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