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From: Heinz Mauelshagen <heinzm@redhat.com>
To: linux-lvm@redhat.com, tomas.dalebjork@gmail.com
Subject: Re: [linux-lvm] size of lvm metadata
Date: Thu, 17 Sep 2020 17:21:58 +0200	[thread overview]
Message-ID: <f4b822a0-33d2-bd9b-6696-09d09aa19052@redhat.com> (raw)
In-Reply-To: <863EB246-CED9-463B-8D52-5A15197A8ABC@gmail.com>

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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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  reply	other threads:[~2020-09-17 15:21 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-16 15:50 Tomas Dalebjörk
2020-09-17 15:21 ` Heinz Mauelshagen [this message]
2020-09-17 17:13   ` Tomas Dalebjörk
2021-12-19 20:13   ` Tomas Dalebjörk

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