From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mimecast-mx02.redhat.com (mimecast02.extmail.prod.ext.rdu2.redhat.com [10.11.55.18]) by smtp.corp.redhat.com (Postfix) with ESMTPS id D01D52166B27 for ; Thu, 17 Sep 2020 17:13:47 +0000 (UTC) Received: from us-smtp-1.mimecast.com (us-smtp-2.mimecast.com [205.139.110.61]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-SHA384 (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 79A82800161 for ; Thu, 17 Sep 2020 17:13:47 +0000 (UTC) From: =?utf-8?Q?Tomas_Dalebj=C3=B6rk?= Mime-Version: 1.0 (1.0) Date: Thu, 17 Sep 2020 19:13:39 +0200 Message-Id: <4529ACB9-3A9B-41F2-9B39-B44DA9768B58@gmail.com> References: In-Reply-To: Content-Type: multipart/alternative; boundary=Apple-Mail-741D5D53-FE27-47FD-A6D9-217AB6C87787 Subject: Re: [linux-lvm] size of lvm metadata Reply-To: LVM general discussion and development List-Id: LVM general discussion and development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , List-Id: To: Heinz Mauelshagen Cc: linux-lvm@redhat.com --Apple-Mail-741D5D53-FE27-47FD-A6D9-217AB6C87787 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable ok Ithanks > pe_count(24) * extent_size(8192) =3D 196608 bytes usable space of the > > total dev_size(204800) metadata size? =3D dev_size(204800) - 196608 =3D > > 8192 Sent from my iPhone > On 17 Sep 2020, at 17:22, Heinz Mauelshagen wrote: >=20 > =EF=BB=BF Tomas, >=20 > 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 w= hich 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). >=20 > On 9/16/20 5:50 PM, Tomas Dalebj=C3=B6rk wrote: > > hi > >=20 > > I am trying to understand how big the lvm metadata is > >=20 > > in the vgcfgbackup file, I can see extent_size =3D 8192 dev_size =3D > > 204800 pe_start =3D 2048 pe_count 24 > >=20 > > pe_count(24) * extent_size(8192) =3D 196608 bytes usable space of the > > total dev_size(204800) metadata size? =3D dev_size(204800) - 196608 =3D > > 8192 > >=20 > > but... pe_start is 2048? so what is pe_start here? cant be > > sectors(512)? bytes? well than ther be not aligned > >=20 > > 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. >=20 > Mind that lvm2 metadata is text formatted (see /etc/lvm/backup/$VGName fo= r 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. >=20 > Heinz >=20 > >=20 > > regards Tomas Sent from my iPhone > >=20 > >=20 > > _______________________________________________ linux-lvm mailing > > list linux-lvm@redhat.com=20 > > https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO > > at http://tldp.org/HOWTO/LVM-HOWTO/ >=20 --Apple-Mail-741D5D53-FE27-47FD-A6D9-217AB6C87787 Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: quoted-printable ok

Ithanks

<= span style=3D"white-space: pre-wrap; display: block; width: 98vw;">pe_count= (24) * extent_size(8192) =3D 196608 bytes usable space of the > total dev_size(204800) metadata size? =3D dev_size(204800) - 196608 = =3D > 8192

Sent fro= m my iPhone

On 17 Sep 2= 020, at 17:22, Heinz Mauelshagen <heinzm@redhat.com> wrote:

=EF=BB=BF =20 =20 =20 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 Dalebj=C3=B6rk wrote:
>= ; hi >=20 > I am trying to understand how big the lvm metadata is >=20 > in the vgcfgbackup file, I can see extent_size =3D 8192 dev_size =3D > 204800 pe_start =3D 2048 pe_count 24 >=20 > pe_count(24) * extent_size(8192) =3D 196608 bytes usable space of the > total dev_size(204800) metadata size? =3D dev_size(204800) - 196608 = =3D > 8192 >=20 > but... pe_start is 2048? so what is pe_start here? cant be > sectors(512)? bytes? well than ther be not aligned >=20 > 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

>= ;=20 > regards Tomas Sent from my iPhone >=20 >=20 > _______________________________________________ linux-lvm mailing > list linux-lvm@redhat.com=20 > https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO > at http://tldp.org/HOWTO/LVM-HOWTO/
=20

--Apple-Mail-741D5D53-FE27-47FD-A6D9-217AB6C87787--