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97 lines
4.1 KiB
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97 lines
4.1 KiB
Plaintext
Wednesday 30th April 2003
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=========================
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A pvmove implementation is now available for the new metadata format.
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When running a command that allocates space (e.g. lvcreate), you can now
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restrict not only which disk(s) may be used but also the Physical Extents
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on those disks. e.g. lvcreate -L 10 vg1 /dev/hda6:1000-2000:3000-4000
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Monday 18th November 2002
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========================
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The new format of LVM metadata is ready for you to test!
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We expect it to be more efficient and more robust than the original format.
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It's more compact and supports transactional changes and replication.
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Should things go wrong on a system, it's human-readable (and editable).
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Please report any problems you find to the mailing list,
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linux-lvm@sistina.com. The software has NOT yet been thoroughly
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tested and so quite possibly there'll still be some bugs in it.
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Be aware of the disclaimer in the COPYING file.
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While testing, we recommend turning logging on in the configuration file
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to provide us with diagnostic information:
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log {
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file="/tmp/lvm2.log"
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level=7
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}
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You should schedule regular backups of your configuration file and
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metadata backups and archives (normally kept under /etc/lvm).
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Please read docs/example.conf and "man lvm.conf" to find out more about
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the configuration file.
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To convert an existing volume group called vg1 to the new format using
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the default settings, use "vgconvert -M2 vg1". See "man vgconvert".
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-M (or --metadatatype in its long form) is a new flag to indicate which
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format of metadata the command should use for anything it creates.
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Currently, the valid types are "lvm1" and "lvm2" and they can be
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abbreviated to "1" and "2" respectively. The default value for this
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flag can be changed in the global section in the config file.
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Backwards-compatible support for the original LVM1 metadata format is
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maintained, but it can be moved into a shared library or removed
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completely with configure's --with-lvm1 option.
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Under LVM2, the basic unit of metadata is the volume group. Different
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volume groups can use different formats of metadata - vg1 could use
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the original LVM1 format while vg2 used the new format - but you can't
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mix formats within a volume group. So to add a PV to an LVM2-format
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volume group you must run "pvcreate -M2" on it, followed by "vgextend".
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With LVM2-format metadata, lvextend will let you specify striping
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parameters. So an LV could consist of two or more "segments" - the
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first segment could have 3 stripes while the second segment has just 2.
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LVM2 maintains a backup of the current metadata for each volume group
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in /etc/lvm/backup, and puts copies of previous versions in
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/etc/lvm/archive. "vgcfgbackup" and "vgcfgrestore" can be used to
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create and restore from these files. If you fully understand what
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you're doing, metadata can be changed by editing a copy of a current
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backup file and using vgcfgrestore to reload it.
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Please read the pvcreate man page for more information on the new
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format for metadata.
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All tools that can change things have a --test flag which can be used
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to check the effect of a set of cmdline args without really making the
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changes.
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What's not finished?
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====================
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The internal cache. If you turn on debugging output you'll see lots of
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repeated disk reads, many of which will eventually get optimised out.
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--test sometimes causes a command to fail (e.g. vgconvert --test) even
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though the real command would work: again, fixing this is waiting for
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the work on the cache.
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Several of the tools do not yet contain the logic to handle full
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recovery: combinations of pvcreate and vgcfgrestore may sometimes be
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needed to restore metadata if a tool gets interrupted or crashes or
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finds something unexpected. This applies particularly to tools that
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work on more than one volume group at once (e.g. vgsplit).
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Display output. Some metadata information cannot yet be displayed.
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Recovery tools to salvage "lost" metadata directly from the disks:
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but we hope the new format will mean such tools are hardly ever needed!
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pvmove will be enhanced to remove the volume group lock so that you can
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run other commands alongside.
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