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Re: [linux-lvm] How to place LVM2 metadata to other disks which don't belong to any volume group?



Hi,

thank for your reply.

I read about "lvm.conf" and "man pvcreate" and practice like your instruction.
but it's hard to meet my expection.

I do as follows:
1, setting lvm.conf to dirs
2, pvcreate --pvmetadatacopies 0
3, vgcreate on pv 
Aborting vg_write: No metadata areas to write to!

I indeed want to  store metadata in common disk such as /dev/sdb, 
eventually to store all vg's metadata to one singe disk which specially used to store metadata without data.

thanks




2013/12/11 Alasdair G Kergon <agk redhat com>
On Wed, Dec 11, 2013 at 03:06:13PM +0800, George Brian wrote:
> Instead of storing metadata on PV metadata areas, now I want to store it to
> other disks which don't belong to any volume group, just common disk.

This can indeed be done but because it is not a configuration that receives
much testing you should check the things you want to do work for you in
your particular circumstances.

LVM needs to use one 512-byte sector on the device to label it as a PV
and store its UUID.  By default the 2nd sector is used as this is normally
free.  Read about --labelsector in 'man pvcreate' and use --pvmetadatacopies 0.

Then read about the 'dirs' setting in the 'metadata' section in 'man lvm.conf':

        dirs  — List of directories holding live copies of LVM2 metadata
        as text files.  These directories must not be  on  logical  vol�\
        umes.   It  is possible to use LVM2 with a couple of directories
        here, preferably on different  (non-logical-volume)  filesystems
        and  with  no  other  on-disk  metadata,  pvmetadatacopies  = 0.
        Alternatively these directories can be in addition  to  the  on-
        disk metadata areas.  This feature was created during the devel�\
        opment of the LVM2 metadata  before  the  new  on-disk  metadata
        areas  were  designed and no longer gets tested.  It is not sup�\
        ported under low-memory conditions, and it is important never to
        edit these metadata files unless you fully understand how things
        work: to make changes you should always use the tools as normal,
        or else vgcfgbackup, edit backup, vgcfgrestore.

Alasdair



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