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lvm2/man/lvconvert.8.in
Mike Snitzer 3e5a54a791 lvconvert --merge @tag support 
Switch lvconvert's --merge code over to using process_each_lv().  Doing
so adds support for a single 'lvconvert --merge' to start merging
multiple LVs (which includes @tag expansion).

Add 'lvconvert --merge @tag' testing to test/t-snapshot-merge.sh

Adjust man/lvconvert.8.in to reflect these expanded capabilities.

The lvconvert.c implementation requires rereading the VG each iteration
of process_each_lv().  Otherwise a stale VG instance associated with
the LV passed to lvconvert_single_merge() would result in stale VG
metadata being written back out to disk.  This overwrote new metadata
that was written when a previous snapshot LV finished merging (via
lvconvert_poll).  This is only an issue when merging multiple LVs that
share the same VG (a single VG is typical for most LVM configurations on
system disks).

In the end this new support is very useful for performing a "system
rollback" that requires multiple snapshot LVs be merged to their
respective origin LV.

The yum-utils 'fs-snapshot' plugin tags all snapshot LVs that it creates
with a common 'snapshot_tag' that is unique to the yum transaction.
Rolling back a yum transaction, that created LVM snapshots with the tag
'yum_20100129133223', is as simple as:
  lvconvert --merge @yum_20100129133223

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2010-02-05 22:44:37 +00:00

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.TH LVCONVERT 8 "LVM TOOLS #VERSION#" "Red Hat, Inc" \" -*- nroff -*-
.SH NAME
lvconvert \- convert a logical volume from linear to mirror or snapshot
.SH SYNOPSIS
.B lvconvert
\-m|\-\-mirrors Mirrors [\-\-mirrorlog {disk|core}] [\-\-corelog] [\-R|\-\-regionsize MirrorLogRegionSize]
[\-A|\-\-alloc AllocationPolicy]
[\-b|\-\-background] [\-f|\-\-force] [\-i|\-\-interval Seconds]
[\-h|\-?|\-\-help]
[\-\-noudevsync]
[\-v|\-\-verbose] [\-y|\-\-yes]
[\-\-version]
.br
LogicalVolume[Path] [PhysicalVolume[Path][:PE[-PE]]...]
.br
.br
.B lvconvert
\-\-splitmirrors Images \-\-name SplitLogicalVolumeName
.br
MirrorLogicalVolume[Path] [SplittablePhysicalVolume[Path][:PE[-PE]]...]
.br
.br
.B lvconvert
\-s|\-\-snapshot [\-c|\-\-chunksize ChunkSize]
[\-h|\-?|\-\-help]
[\-\-noudevsync]
[\-v|\-\-verbose]
[\-Z|\-\-zero y|n]
[\-\-version]
.br
OriginalLogicalVolume[Path] SnapshotLogicalVolume[Path]
.br
.br
.B lvconvert
\-\-merge [\-b|\-\-background] [\-i|\-\-interval Seconds]
[\-h|\-?|\-\-help]
[\-v|\-\-verbose]
[\-\-version]
SnapshotLogicalVolume[Path]...
.br
.br
.B lvconvert
\-\-repair
[\-h|\-?|\-\-help]
[\-v|\-\-verbose]
[\-\-version]
LogicalVolume[Path] [PhysicalVolume[Path]...]
.SH DESCRIPTION
lvconvert will change a linear logical volume to a mirror
logical volume or to a snapshot of linear volume and vice versa.
It is also used to add and remove disk logs from mirror devices.
.br
If the conversion requires allocation of physical extents (for
example, when converting from linear to mirror) and you specify
one or more PhysicalVolumes (optionally with ranges of physical
extents), allocation of physical extents will be restricted to
these physical extents. If the conversion frees physical extents
(for example, when converting from a mirror to a linear, or reducing
mirror legs) and you specify one or more PhysicalVolumes,
the freed extents come first from the specified PhysicalVolumes.
.SH OPTIONS
See \fBlvm\fP for common options.
.br
Exactly one of \-\-splitmirrors, \-\-mirrors, \-\-repair, \-\-snapshot
or \-\-merge arguments is required.
.br
.TP
.I \-m, \-\-mirrors Mirrors
Specifies the degree of the mirror you wish to create.
For example, "-m 1" would convert the original logical
volume to a mirror volume with 2-sides; that is, a
linear volume plus one copy.
.TP
.I \-\-mirrorlog {disk|core}
Specifies the type of log to use.
The default is disk, which is persistent and requires
a small amount of storage space, usually on a separate device
from the data being mirrored.
Core may be useful for short-lived mirrors: It means the mirror is
regenerated by copying the data from the first device again every
time the device is activated - perhaps, for example, after every reboot.
.TP
.I \-\-corelog
The optional argument "--corelog" is the same as specifying "--mirrorlog core".
.TP
.I \-R, \-\-regionsize MirrorLogRegionSize
A mirror is divided into regions of this size (in MB), and the mirror log
uses this granularity to track which regions are in sync.
.TP
.I \-b, \-\-background
Run the daemon in the background.
.TP
.I \-i, \-\-interval Seconds
Report progress as a percentage at regular intervals.
.br
.TP
.I \-\-noudevsync
Disable udev synchronisation. The
process will not wait for notification from udev.
It will continue irrespective of any possible udev processing
in the background. You should only use this if udev is not running
or has rules that ignore the devices LVM2 creates.
.br
.TP
.I \-\-splitmirrors Images
The number of redundant Images of a mirror to be split off and used
to form a new logical volume. A name must be supplied for the
newly-split-off logical volume using the \-\-name argument.
.TP
.I \-n Name
The name to apply to a logical volume which has been split off from
a mirror logical volume.
.br
.TP
.I \-s, \-\-snapshot
Create a snapshot from existing logical volume using another
existing logical volume as its origin.
.TP
.I \-c, \-\-chunksize ChunkSize
Power of 2 chunk size for the snapshot logical volume between 4k and 512k.
.TP
.I \-Z, \-\-zero y|n
Controls zeroing of the first KB of data in the snapshot.
If the volume is read-only the snapshot will not be zeroed.
.TP
.I \-\-merge
Merges a snapshot into its origin volume. If both the origin and snapshot volume
are not open the merge will start immediately. Otherwise, the merge will start
the first time either the origin or snapshot are activated and both are closed.
Merging a snapshot into an origin that cannot be closed, for example a root
filesystem, is deferred until the next time the origin volume is activated.
When merging starts, the resulting logical volume will have the origin's name,
minor number and UUID. While the merge is in progress, reads or writes to the
origin appear as they were directed to the snapshot being merged. When the
merge finishes, the merged snapshot is removed. Multiple snapshots may
be specified on the commandline or a @tag may be used to specify
multiple snapshots be merged to their respective origin.
.br
.TP
.I \-\-repair
Repair a mirror after suffering a disk failure. The mirror will be brought back
into a consistent state. By default, the original number of mirrors will be
restored if possible. Specify \-y on the command line to skip the prompts.
Use \-f if you do not want any replacement. Additionally, you may use
\-\-use-policies to use the device replacement policy specified in lvm.conf,
viz. activation/mirror_log_fault_policy or
activation/mirror_device_fault_policy.
.br
.SH Examples
"lvconvert -m1 vg00/lvol1"
.br
converts the linear logical volume "vg00/lvol1" to
a two-way mirror logical volume.
"lvconvert --mirrorlog core vg00/lvol1"
.br
converts a mirror with a disk log to a
mirror with an in-memory log.
"lvconvert --mirrorlog disk vg00/lvol1"
.br
converts a mirror with an in-memory log
to a mirror with a disk log.
"lvconvert -m0 vg00/lvol1"
.br
converts a mirror logical volume to a linear logical
volume.
.br
.br
"lvconvert -s vg00/lvol1 vg00/lvol2"
.br
converts logical volume "vg00/lvol2" to snapshot of original volume "vg00/lvol1"
.br
"lvconvert -m1 vg00/lvol1 /dev/sda:0-15 /dev/sdb:0-15"
.br
converts linear logical volume "vg00/lvol1" to a two-way mirror, using physical
extents /dev/sda:0-15 and /dev/sdb:0-15 for allocation of new extents.
.br
"lvconvert -m0 vg00/lvmirror1 /dev/sda
.br
converts mirror logical volume "vg00/lvmirror1" to linear, freeing physical
extents from /dev/sda.
.br
"lvconvert --merge vg00/lvol1_snap"
.br
merges "vg00/lvol1_snap" into its origin.
.br
"lvconvert --merge @some_tag"
.br
If vg00/lvol1, vg00/lvol2, and vg00/lvol3 are all tagged with "some_tag"
each snapshot logical volume will be merged serially, e.g.: vg00/lvol1,
then vg00/lvol2, then vg00/lvol3. If --background were used it would start
all snapshot logical volume merges in parallel.
.SH SEE ALSO
.BR lvm (8),
.BR vgcreate (8),
.BR lvremove (8),
.BR lvrename (8),
.BR lvextend (8),
.BR lvreduce (8),
.BR lvdisplay (8),
.BR lvscan (8)
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