lvm2/man/lvm.8.in

.TH LVM 8 "LVM TOOLS #VERSION#" "Sistina Software UK" \" -*- nroff -*-
.SH NAME
lvm \- LVM2 tools
.SH SYNOPSIS
.B lvm
[command | file]
.SH DESCRIPTION
lvm provides the command-line tools for LVM2.  A separate
manual page describes each command in detail.
.LP
If \fBlvm\fP is invoked with no arguments it presents a readline prompt
(assuming it was compiled with readline support).
LVM commands may be entered interactively at this prompt with
readline facilities including history and command name and option
completion.  Refer to \fBreadline\fP(3) for details.
.LP
If \fBlvm\fP is invoked with argv[0] set to the name of a specific
LVM command (for example by using a hard or soft link) it acts as
that command.
.LP
On invocation, \fBlvm\fP requires that only the standard file descriptors
stdin, stdout and stderr are available.  If others are found, they
get closed and messages are issued warning about the leak.
This warning can be suppressed by setting the environment variable
.B LVM_SUPPRESS_FD_WARNINGS\fP.
.LP
Where commands take VG or LV names as arguments, the full path name is
optional.  An LV called "lvol0" in a VG called "vg0" can be specified
as "vg0/lvol0".  Where a list of VGs is required but is left empty,
a list of all VGs will be substituted.  Where a list of LVs is required
but a VG is given, a list of all the LVs in that VG will be substituted.
So \fBlvdisplay vg0\fP will display all the LVs in "vg0".
Tags can also be used - see \fB\-\-addtag\fP below.
.LP
One advantage of using the built-in shell is that configuration
information gets cached internally between commands.
.LP
A file containing a simple script with one command per line
can also be given on the command line.  The script can also be
executed directly if the first line is #! followed by the absolute
path of \fBlvm\fP.
.SH BUILT-IN COMMANDS
The following commands are built into lvm without links normally
being created in the filesystem for them.
.TP
\fBdumpconfig\fP \(em Display the configuration information after
loading \fBlvm.conf\fP(5) and any other configuration files.
.TP
\fBdevtypes\fP \(em Display the recognised built-in block device types.
.TP
\fBformats\fP \(em Display recognised metadata formats.
.TP
\fBhelp\fP \(em Display the help text.
.TP
\fBpvdata\fP \(em Not implemented in LVM2.
.TP
\fBsegtypes\fP \(em Display recognised Logical Volume segment types.
.TP
\fBtags\fP \(em Display any tags defined on this host.
.TP
\fBversion\fP \(em Display version information.
.LP
.SH COMMANDS
The following commands implement the core LVM functionality.
.TP
\fBpvchange\fP \(em Change attributes of a Physical Volume.
.TP
\fBpvck\fP \(em Check Physical Volume metadata.
.TP
\fBpvcreate\fP \(em Initialize a disk or partition for use by LVM.
.TP
\fBpvdisplay\fP \(em Display attributes of a Physical Volume.
.TP
\fBpvmove\fP \(em Move Physical Extents.
.TP
\fBpvremove\fP \(em Remove a Physical Volume.
.TP
\fBpvresize\fP \(em Resize a disk or partition in use by LVM2.
.TP
\fBpvs\fP \(em Report information about Physical Volumes.
.TP
\fBpvscan\fP \(em Scan all disks for Physical Volumes.
.TP
\fBvgcfgbackup\fP \(em Backup Volume Group descriptor area.
.TP
\fBvgcfgrestore\fP \(em Restore Volume Group descriptor area.
.TP
\fBvgchange\fP \(em Change attributes of a Volume Group.
.TP
\fBvgck\fP \(em Check Volume Group metadata.
.TP
\fBvgconvert\fP \(em Convert Volume Group metadata format.
.TP
\fBvgcreate\fP \(em Create a Volume Group.
.TP
\fBvgdisplay\fP \(em Display attributes of Volume Groups.
.TP
\fBvgexport\fP \(em Make volume Groups unknown to the system.
.TP
\fBvgextend\fP \(em Add Physical Volumes to a Volume Group.
.TP
\fBvgimport\fP \(em Make exported Volume Groups known to the system.
.TP
\fBvgimportclone\fP \(em Import and rename duplicated Volume Group (e.g. a hardware snapshot).
.TP
\fBvgmerge\fP \(em Merge two Volume Groups.
.TP
\fBvgmknodes\fP \(em Recreate Volume Group directory and Logical Volume special files
.TP
\fBvgreduce\fP \(em Reduce a Volume Group by removing one or more
Physical Volumes.
.TP
\fBvgremove\fP \(em Remove a Volume Group.
.TP
\fBvgrename\fP \(em Rename a Volume Group.
.TP
\fBvgs\fP \(em Report information about Volume Groups.
.TP
\fBvgscan\fP \(em Scan all disks for Volume Groups and rebuild caches.
.TP
\fBvgsplit\fP \(em Split a Volume Group into two, moving any logical
volumes from one Volume Group to another by moving entire Physical
Volumes.
.TP
\fBlvchange\fP \(em Change attributes of a Logical Volume.
.TP
\fBlvconvert\fP \(em Convert a Logical Volume from linear to mirror or snapshot.
.TP
\fBlvcreate\fP \(em Create a Logical Volume in an existing Volume Group.
.TP
\fBlvdisplay\fP \(em Display attributes of a Logical Volume.
.TP
\fBlvextend\fP \(em Extend the size of a Logical Volume.
.TP
\fBlvmchange\fP \(em Change attributes of the Logical Volume Manager.
.TP
\fBlvmdiskscan\fP \(em Scan for all devices visible to LVM2.
.TP
\fBlvmdump\fP \(em Create lvm2 information dumps for diagnostic purposes.
.TP
\fBlvreduce\fP \(em Reduce the size of a Logical Volume.
.TP
\fBlvremove\fP \(em Remove a Logical Volume.
.TP
\fBlvrename\fP \(em Rename a Logical Volume.
.TP
\fBlvresize\fP \(em Resize a Logical Volume.
.TP
\fBlvs\fP \(em Report information about Logical Volumes.
.TP
\fBlvscan\fP \(em Scan (all disks) for Logical Volumes.
.TP
The following commands are not implemented in LVM2 but might be in the future: lvmsadc, lvmsar, pvdata.
.SH OPTIONS
The following options are available for many of the commands.
They are implemented generically and documented here rather
than repeated on individual manual pages.
.TP
.BR \-h ", " \-? ", " \-\-help
Display the help text.
.TP
.B \-\-version
Display version information.
.TP
.BR \-v ", " \-\-verbose
Set verbose level. Repeat from 1 to 3 times to increase the detail
of messages sent to stdout and stderr.  Overrides config file setting.
.TP
.BR \-d ", " \-\-debug
Set debug level. Repeat from 1 to 6 times to increase the detail of
messages sent to the log file and/or syslog (if configured).
Overrides config file setting.
.TP
.BR \-q ", "  \-\-quiet
Suppress output and log messages.
Overrides \fB\-d\fP and \fB\-v\fP.
.TP
.BR \-\-yes
Don't prompt for confirmation interactively but instead always assume the
answer is 'yes'.  Take great care if you use this!
.TP
.BR \-t ", " \-\-test
Run in test mode. Commands will not update metadata.
This is implemented by disabling all metadata writing but nevertheless
returning success to the calling function.  This may lead to unusual
error messages in multi-stage operations if a tool relies on reading
back metadata it believes has changed but hasn't.
.TP
.BR \-\-driverloaded " {" \fIy | \fIn }
Whether or not the device-mapper kernel driver is loaded.
If you set this to \fIn\fP, no attempt will be made to contact the driver.
.TP
.BR \-A ", " \-\-autobackup " {" \fIy | \fIn }
Whether or not to metadata should be backed up automatically after a change.
You are strongly advised not to disable this!
See \fBvgcfgbackup\fP(8).
.TP
.BR \-P ", " \-\-partial
When set, the tools will do their best to provide access to Volume Groups
that are only partially available (one or more Physical Volumes belonging
to the Volume Group are missing from the system).  Where part of a logical
volume is missing, \fB/dev/ioerror\fP will be substituted, and you could use
\fBdmsetup\fP(8) to set this up to return I/O errors when accessed,
or create it as a large block device of nulls.  Metadata may not be
changed with this option. To insert a replacement Physical Volume
of the same or large size use \fBpvcreate \-u\fP to set the uuid to
match the original followed by \fBvgcfgrestore\fP(8).
.TP
.BR \-M ", " \-\-metadatatype " " \fIType
Specifies which type of on-disk metadata to use, such as \fIlvm1\fP
or \fIlvm2\fP, which can be abbreviated to \fI1\fP or \fI2\fP respectively.
The default (\fIlvm2\fP) can be changed by setting \fBformat\fP
in the \fBglobal\fP section of the config file.
.TP
.B \-\-ignorelockingfailure
This lets you proceed with read-only metadata operations such as
\fBlvchange \-ay\fP and \fBvgchange \-ay\fP even if the locking module fails.
One use for this is in a system init script if the lock directory
is mounted read-only when the script runs.
.TP
.B \-\-ignoreskippedcluster
Use to avoid exiting with an non-zero status code if the command is run
without clustered locking and some clustered Volume Groups have to be
skipped over.
.TP
.B \-\-addtag \fITag
Add the tag \fITag\fP to a PV, VG or LV.
Supply this argument multiple times to add more than one tag at once.
A tag is a word that can be used to group LVM2 objects of the same type
together.
Tags can be given on the command line in place of PV, VG or LV
arguments.  Tags should be prefixed with @ to avoid ambiguity.
Each tag is expanded by replacing it with all objects possessing
that tag which are of the type expected by its position on the command line.
PVs can only possess tags while they are part of a Volume Group:
PV tags are discarded if the PV is removed from the VG.
As an example, you could tag some LVs as \fBdatabase\fP and others
as \fBuserdata\fP and then activate the database ones
with \fBlvchange \-ay @database\fP.
Objects can possess multiple tags simultaneously.
Only the new LVM2 metadata format supports tagging: objects using the
LVM1 metadata format cannot be tagged because the on-disk format does not
support it.
Characters allowed in tags are:
.B A-Z a-z 0-9 _ + . -
and as of version 2.02.78 the following characters are also accepted:
.B / = ! : # &
.TP
.B \-\-deltag \fITag
Delete the tag \fITag\fP from a PV, VG or LV, if it's present.
Supply this argument multiple times to remove more than one tag at once.
.TP
.IR \fB\-\-alloc \ { anywhere | contiguous | cling | inherit | normal }
Selects the allocation policy when a command needs to allocate
Physical Extents from the Volume Group.
Each Volume Group and Logical Volume has an allocation policy defined.
The default for a Volume Group is \fInormal\fP which applies
common-sense rules such as not placing parallel stripes on the same
Physical Volume.  The default for a Logical Volume is \fIinherit\fP
which applies the same policy as for the Volume Group.  These policies can
be changed using \fBlvchange\fP(8) and \fBvgchange\fP(8) or overridden
on the command line of any command that performs allocation.
The \fIcontiguous\fP policy requires that new Physical Extents be placed adjacent
to existing Physical Extents.
The \fIcling\fP policy places new Physical Extents on the same Physical
Volume as existing Physical Extents in the same stripe of the Logical Volume.
If there are sufficient free Physical Extents to satisfy
an allocation request but \fInormal\fP doesn't use them,
\fIanywhere\fP will - even if that reduces performance by
placing two stripes on the same Physical Volume.
.TP
.IR \fB\-\-profile \ ProfileName
Selects the configuration profile to use when processing an LVM command.
In addition to that, when creating a Volume Group or a Logical Volume,
it causes the ProfileName to be stored in metadata for each Volume Group
or Logical Volume. If the profile is stored in metadata, it is automatically
applied next time the Volume Group or the Logical Volume is processed and the
use of --profile is not necessary when running LVM commands further. See also
\fBlvm.conf\fP(5) for more information about \fBprofile config\fP and the
way it fits with other LVM configuration methods.
.TP
.IR \fB\-\-config \ ConfigurationString
Uses the ConfigurationString as direct string representation of the configuration
to override the existing configuration. The ConfigurationString is of exactly
the same format as used in any LVM configuration file. See \fBlvm.conf\fP(5)
for more information about \fBdirect config override on command line\fP and the
way it fits with other LVM configuration methods.
.SH ENVIRONMENT VARIABLES
.TP
.B HOME
Directory containing \fI.lvm_history\fP if the internal readline
shell is invoked.
.TP
.B LVM_SYSTEM_DIR
Directory containing \fBlvm.conf\fP(5) and other LVM system files.
Defaults to "#DEFAULT_SYS_DIR#".
.TP
.B LVM_SUPPRESS_FD_WARNINGS
Suppress warnings about openned file descriptors, when lvm command
is executed.
.TP
.B LVM_VG_NAME
The Volume Group name that is assumed for
any reference to a Logical Volume that doesn't specify a path.
Not set by default.
.TP
.B LVM_LVMETAD_PIDFILE
Path for the lvmetad pid file.
.TP
.B LVM_LVMETAD_SOCKET
Path for the lvmetad socket file.
.SH VALID NAMES
The following characters are valid for VG and LV names:
.B a-z A-Z 0-9 + _ . -
.LP
VG and LV names cannot begin with a hyphen.
There are also various reserved names that are used internally by lvm that can not be used as LV or VG names.
A VG cannot be called anything that exists in /dev/ at the time of creation, nor can it be called '.' or '..'.
A LV cannot be called '.' '..' 'snapshot' or 'pvmove'. The LV name may also not contain
the strings '_mlog', '_mimage', '_rimage', '_tdata', '_tmeta'.
.SH ALLOCATION
When an operation needs to allocate Physical Extents for one or more
Logical Volumes, the tools proceed as follows:

First of all, they generate the complete set of unallocated Physical Extents
in the Volume Group.  If any ranges of Physical Extents are supplied at
the end of the command line, only unallocated Physical Extents within
those ranges on the specified Physical Volumes are considered.

Then they try each allocation policy in turn, starting with the strictest
policy (\fIcontiguous\fP) and ending with the allocation policy specified
using \fB\-\-alloc\fP or set as the default for the particular Logical
Volume or Volume Group concerned.  For each policy, working from the
lowest-numbered Logical Extent of the empty Logical Volume space that
needs to be filled, they allocate as much space as possible according to
the restrictions imposed by the policy.  If more space is needed,
they move on to the next policy.

The restrictions are as follows:

\fIContiguous\fP requires that the physical location of any Logical
Extent that is not the first Logical Extent of a Logical Volume is
adjacent to the physical location of the Logical Extent immediately
preceding it.

\fICling\fP requires that the Physical Volume used for any Logical
Extent to be added to an existing Logical Volume is already in use by at
least one Logical Extent earlier in that Logical Volume.  If the
configuration parameter allocation/cling_tag_list is defined, then two
Physical Volumes are considered to match if any of the listed tags is
present on both Physical Volumes.  This allows groups of Physical
Volumes with similar properties (such as their physical location) to be
tagged and treated as equivalent for allocation purposes.

When a Logical Volume is striped or mirrored, the above restrictions are
applied independently to each stripe or mirror image (leg) that needs
space.

\fINormal\fP will not choose a Physical Extent that shares the same Physical
Volume as a Logical Extent already allocated to a parallel Logical
Volume (i.e. a different stripe or mirror image/leg) at the same offset 
within that parallel Logical Volume.

When allocating a mirror log at the same time as Logical Volumes to hold
the mirror data, Normal will first try to select different Physical
Volumes for the log and the data.  If that's not possible and the
allocation/mirror_logs_require_separate_pvs configuration parameter is
set to 0, it will then allow the log to share Physical Volume(s) with
part of the data.  

When allocating thin pool metadata, similar considerations to those of a
mirror log in the last paragraph apply based on the value of the
allocation/thin_pool_metadata_require_separate_pvs configuration
parameter.

If you rely upon any layout behaviour beyond that documented here, be
aware that it might change in future versions of the code.  

For example, if you supply on the command line two empty Physical
Volumes that have an identical number of free Physical Extents available for
allocation, the current code considers using each of them in the order
they are listed, but there is no guarantee that future releases will
maintain that property.  If it is important to obtain a specific layout
for a particular Logical Volume, then you should build it up through a
sequence of \fBlvcreate\fP(8) and \fBlvconvert\fP(8) steps such that the
restrictions described above applied to each step leave the tools no
discretion over the layout.

To view the way the allocation process currently works in any specific
case, read the debug logging output, for example by adding \fB\-vvvv\fP to
a command.

.SH ADVANCED LOGICAL VOLUME TYPES
Some logical volume types are simple to create and can be done with a
single \fBlvcreate\fP(8) command.  The linear and striped logical
volume types are an example of this.  Other logical volume types may
require more than one command to create.  The cache and thinly provisioned
types are examples of this.  This section is devoted to explaining the
creation and monitoring of the more advanced types of logical volumes in
LVM.  While the specifics of each command can be found in their respective
man page, here you will find examples and best practices that may invoke
multiple commands.
.br
.SS Cache Logical Volumes
A cache logical volume is one that allows a small and fast block device to
be used to improve the performance of larger and slower block devices.  It
does this by storing the more frequently used blocks on the faster device.
LVM refers to the small fast device as a "cache pool".  The large slow device
is called the "origin".  Due to requirements from dm-cache (the kernel
driver), LVM further splits the "cache pool" into two devices - the "cache pool
metadata" and "cache pool data" devices.  The "cache pool data" device is where
copies of data blocks are kept from the origin to increase speed.  The "cache
pool metadata" device holds the accounting information that specifies where
data blocks are stored (e.g. on the "origin" or in the "cache pool data" device).
Users should be familiar with these three devices should they wish to create
the best and most robust cached logical volumes.

.SS Creating Cache Logical Volumes
The steps to create a logical volume of cache type are as follows:
.TP
1)
Create the cache pool's data device.  The size of this device directly
correlates to the size of the cache and will ultimately be reported as
the size of the cache pool.
.TP
2)
Create the cache pool's metadata device.  The size of this device is
loosely related to the size of the data device.  Generally, a user can
size this 1000 times smaller than the cache pool data device with a
minimum size of 8MiB.
.TP
3)
Create the cache pool by combining the cache pool data and metadata
logical volumes created in steps 1 & 2.  When performing this step,
the user can specify behavioral characteristics of the cache pool if
they wish.  If no new name is specified when combining, the name of the
cache pool data device will become the name of the cachepool.  The sub-LVs
are then renamed to <name>_cdata and <name>_cmeta.
.TP
4)
Create a cached logical volume by linking the cache pool to an existing
logical volume.  The user accessible cached LV keeps the name of the origin,
while the actual origin device becomes a hidden LV with the name
<origial name>_corig.  Users can perform this step while the device which
is to be cached is in use.

.P
The above steps represent the best way to create a cached logical volume.
They provide access to the most options and have the ability to create the
most robust logical volumes.  The examples below will illustrate how these
steps might be used in practice.

.B Example 1:
Creating a simple cache device named, "my_lv".
.br

.nf
# Create a device we wish to cache (yours may already exist)
Step-0> lvcreate -L 10G -n my_lv my_vg /dev/slow_dev

# Create a cache pool data LV
Step-1> lvcreate -L 1G -n cachepool my_vg /dev/fast_dev

# Create a cache pool metadata LV (~1/1000th size of pool data)
Step-2> lvcreate -L 8M -n meta my_vg /dev/fast_dev

# Combine cache pool sub-LVs into a cache pool.
Step-3> lvconvert --type cache_pool vg/cachepool --poolmetadata vg/meta

# Combine the cache pool and origin to create a cached LV
Step-4> lvconvert --type cache my_vg/my_lv --cachepool vg/cachepool
.fi

Users who are concerned about the possibility of failures in their fast devices
that could lead to data loss might consider making their cache pool sub-LVs
redundant.  Example 2 illustrates how to do just that.  Note that only steps
1 & 2 change slightly.

.B Example 2:
Creating a cache LV with a fault tolerant cache pool.

.nf
# Create a device we wish to cache (yours may already exist)
Step-0> lvcreate -L 10G -n my_lv my_vg /dev/slow_dev

# Create a 2-way RAID1 cache pool data LV
Step-01> lvcreate --type raid1 -L 1G -n cachepool my_vg /dev/fast[12]

# Create a 2-way RAID1 cache pool metadata LV
Step-2> lvcreate --type raid1 -L 8M -n meta my_vg /dev/fast1 /dev/fast2

# Combine cache pool sub-LVs into a cache pool.
Step-3> lvconvert --type cache_pool vg/cachepool --poolmetadata vg/meta

# Combine the cache pool and origin to create a cached LV
Step-4> lvconvert --type cache my_vg/my_lv --cachepool vg/cachepool
.fi

Some users wish to ensure that any data written will be stored both in the
cache pool and on the origin.  The loss of the cache device in this case
would not mean the loss of any data.  When combining the cache pool's sub-LVs
to form the cachepool, behavioral characteristics of the cache can be
specified - in this case, writethrough vs. writeback.  Note that only step
3 is affected in this case.

.B Example 3:
Creating a simple cache device with "writethough" caching.

.nf
# Create a device we wish to cache (yours may already exist)
Step-0> lvcreate -L 10G -n my_lv my_vg /dev/slow_dev

# Create a cache pool data LV
Step-1> lvcreate -L 1G -n cachepool my_vg /dev/fast_dev

# Create a cache pool metadata LV
Step-2> lvcreate -L 8M -n meta my_vg /dev/fast_dev

# Combine cache pool sub-LVs into a cache pool and specify "writethough".
Step-3> lvconvert --type cache_pool vg/cachepool \\
	--poolmetadata vg/meta --cachemode writethrough -n cachepool

# Combine the cache pool and origin to create a cached LV
Step-4> lvconvert --type cache my_vg/my_lv --cachepool vg/cachepool
.fi

.SS Removing Cache Logical Volumes
If users wish to remove all logical volumes associated with a cached
logical volume, they must remove both top-level, user visible devices.
The cache pool metadata and data logical volumes cannot be removed
directly.  If only the cache pool is specfied for removal, any cached
blocks not yet on the origin will be flush, the cache pool will be
removed, and the now un-cached origin will remain.  If the user
specifies a cached LV for removal, then the origin device is
removed and only the cache pool will remain.  The cache pool can then be
used to create another cache LV with a different origin if desired.

When users intend to remove all logical volumes associated with a
cached LV, it is generally better to start with the origin and then
remove the cache pool.  If the operations are performed in the
reverse order, the user will have to wait for the contents of the
cache pool to be flushed before they remove the origin.  This
could take some time.

.SH DIAGNOSTICS
All tools return a status code of zero on success or non-zero on failure.
.SH FILES
.I #DEFAULT_SYS_DIR#/lvm.conf
.br
.I $HOME/.lvm_history
.SH SEE ALSO
.BR lvm.conf (5),
.BR clvmd (8),
.BR lvchange (8),
.BR lvcreate (8),
.BR lvdisplay (8),
.BR lvextend (8),
.BR lvmchange (8),
.BR lvmdiskscan (8),
.BR lvreduce (8),
.BR lvremove (8),
.BR lvrename (8),
.BR lvresize (8),
.BR lvs (8),
.BR lvscan (8),
.BR pvchange (8),
.BR pvck (8),
.BR pvcreate (8),
.BR pvdisplay (8),
.BR pvmove (8),
.BR pvremove (8),
.BR pvs (8),
.BR pvscan (8),
.BR vgcfgbackup (8),
.BR vgchange  (8),
.BR vgck (8),
.BR vgconvert (8),
.BR vgcreate (8),
.BR vgdisplay (8),
.BR vgextend (8),
.BR vgimport (8),
.BR vgimportclone (8),
.BR vgmerge (8),
.BR vgmknodes (8),
.BR vgreduce (8),
.BR vgremove (8),
.BR vgrename (8),
.BR vgs (8),
.BR vgscan (8),
.BR vgsplit (8),
.BR readline (3)