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lvm(8) [centos man page]

LVM(8)							      System Manager's Manual							    LVM(8)

NAME
lvm - LVM2 tools SYNOPSIS
lvm [command | file] DESCRIPTION
lvm provides the command-line tools for LVM2. A separate manual page describes each command in detail. If lvm 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 read- line(3) for details. If lvm 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 com- mand. On invocation, lvm 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 LVM_SUP- PRESS_FD_WARNINGS. 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 speci- fied 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 lvdisplay vg0 will display all the LVs in "vg0". Tags can also be used - see --addtag below. One advantage of using the built-in shell is that configuration information gets cached internally between commands. 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 lvm. BUILT-IN COMMANDS The following commands are built into lvm without links normally being created in the filesystem for them. dumpconfig -- Display the configuration information after loading lvm.conf(5) and any other configuration files. devtypes -- Display the recognised built-in block device types. formats -- Display recognised metadata formats. help -- Display the help text. pvdata -- Not implemented in LVM2. segtypes -- Display recognised Logical Volume segment types. tags -- Display any tags defined on this host. version -- Display version information. COMMANDS
The following commands implement the core LVM functionality. pvchange -- Change attributes of a Physical Volume. pvck -- Check Physical Volume metadata. pvcreate -- Initialize a disk or partition for use by LVM. pvdisplay -- Display attributes of a Physical Volume. pvmove -- Move Physical Extents. pvremove -- Remove a Physical Volume. pvresize -- Resize a disk or partition in use by LVM2. pvs -- Report information about Physical Volumes. pvscan -- Scan all disks for Physical Volumes. vgcfgbackup -- Backup Volume Group descriptor area. vgcfgrestore -- Restore Volume Group descriptor area. vgchange -- Change attributes of a Volume Group. vgck -- Check Volume Group metadata. vgconvert -- Convert Volume Group metadata format. vgcreate -- Create a Volume Group. vgdisplay -- Display attributes of Volume Groups. vgexport -- Make volume Groups unknown to the system. vgextend -- Add Physical Volumes to a Volume Group. vgimport -- Make exported Volume Groups known to the system. vgimportclone -- Import and rename duplicated Volume Group (e.g. a hardware snapshot). vgmerge -- Merge two Volume Groups. vgmknodes -- Recreate Volume Group directory and Logical Volume special files vgreduce -- Reduce a Volume Group by removing one or more Physical Volumes. vgremove -- Remove a Volume Group. vgrename -- Rename a Volume Group. vgs -- Report information about Volume Groups. vgscan -- Scan all disks for Volume Groups and rebuild caches. vgsplit -- Split a Volume Group into two, moving any logical volumes from one Volume Group to another by moving entire Physical Volumes. lvchange -- Change attributes of a Logical Volume. lvconvert -- Convert a Logical Volume from linear to mirror or snapshot. lvcreate -- Create a Logical Volume in an existing Volume Group. lvdisplay -- Display attributes of a Logical Volume. lvextend -- Extend the size of a Logical Volume. lvmchange -- Change attributes of the Logical Volume Manager. lvmdiskscan -- Scan for all devices visible to LVM2. lvmdump -- Create lvm2 information dumps for diagnostic purposes. lvreduce -- Reduce the size of a Logical Volume. lvremove -- Remove a Logical Volume. lvrename -- Rename a Logical Volume. lvresize -- Resize a Logical Volume. lvs -- Report information about Logical Volumes. lvscan -- Scan (all disks) for Logical Volumes. The following commands are not implemented in LVM2 but might be in the future: lvmsadc, lvmsar, pvdata. 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. -h, -?, --help Display the help text. --version Display version information. -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. -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. -q, --quiet Suppress output and log messages. Overrides -d and -v. --yes Don't prompt for confirmation interactively but instead always assume the answer is 'yes'. Take great care if you use this! -t, --test Run in test mode. Commands will not update metadata. This is implemented by disabling all metadata writing but nevertheless return- ing 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. --driverloaded {y|n} Whether or not the device-mapper kernel driver is loaded. If you set this to n, no attempt will be made to contact the driver. -A, --autobackup {y|n} Whether or not to metadata should be backed up automatically after a change. You are strongly advised not to disable this! See vgcfgbackup(8). -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, /dev/ioerror will be substituted, and you could use dmsetup(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 pvcreate -u to set the uuid to match the original followed by vgcfgrestore(8). -M, --metadatatype Type Specifies which type of on-disk metadata to use, such as lvm1 or lvm2, which can be abbreviated to 1 or 2 respectively. The default (lvm2) can be changed by setting format in the global section of the config file. --ignorelockingfailure This lets you proceed with read-only metadata operations such as lvchange -ay and vgchange -ay 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. --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. --addtag Tag Add the tag Tag 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 database and others as userdata and then activate the database ones with lvchange -ay @database. 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 sup- port it. Characters allowed in tags are: A-Z a-z 0-9 _ + . - and as of version 2.02.78 the following characters are also accepted: / = ! : # & --deltag Tag Delete the tag Tag from a PV, VG or LV, if it's present. Supply this argument multiple times to remove more than one tag at once. --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 Logi- cal Volume has an allocation policy defined. The default for a Volume Group is normal which applies common-sense rules such as not placing parallel stripes on the same Physical Volume. The default for a Logical Volume is inherit which applies the same policy as for the Volume Group. These policies can be changed using lvchange(8) and vgchange(8) or overridden on the command line of any com- mand that performs allocation. The contiguous policy requires that new Physical Extents be placed adjacent to existing Physical Extents. The cling 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 normal doesn't use them, anywhere will - even if that reduces performance by placing two stripes on the same Physical Volume. --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 lvm.conf(5) for more information about profile config and the way it fits with other LVM configuration methods. --config ConfigurationString Uses the ConfigurationString as direct string representation of the configuration to override the existing configuration. The Con- figurationString is of exactly the same format as used in any LVM configuration file. See lvm.conf(5) for more information about direct config override on command line and the way it fits with other LVM configuration methods. ENVIRONMENT VARIABLES
HOME Directory containing .lvm_history if the internal readline shell is invoked. LVM_SYSTEM_DIR Directory containing lvm.conf(5) and other LVM system files. Defaults to "/etc/lvm". LVM_SUPPRESS_FD_WARNINGS Suppress warnings about openned file descriptors, when lvm command is executed. 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. LVM_LVMETAD_PIDFILE Path for the lvmetad pid file. LVM_LVMETAD_SOCKET Path for the lvmetad socket file. VALID NAMES
The following characters are valid for VG and LV names: a-z A-Z 0-9 + _ . - 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 can- not be called '.' '..' 'snapshot' or 'pvmove'. The LV name may also not contain the strings '_mlog', '_mimage', '_rimage', '_tdata', '_tmeta'. 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 con- sidered. Then they try each allocation policy in turn, starting with the strictest policy (contiguous) and ending with the allocation policy speci- fied using --alloc 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: Contiguous 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. Cling 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. Normal 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 Physi- cal 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 lvcreate(8) and lvconvert(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 -vvvv to a command. LOGICAL VOLUME TYPES
Some logical volume types are simple to create and can be done with a single lvcreate(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 thin provisioning types are examples of this. Cache The cache logical volume type uses a small and fast LV to improve the performance of a large and slow LV. It does this by storing the fre- quently used blocks on the faster LV. LVM refers to the small fast LV as a cache pool LV. The large slow LV is called the origin LV. Due to requirements from dm-cache (the kernel driver), LVM further splits the cache pool LV into two devices - the cache data LV and cache metadata LV. The cache data LV is where copies of data blocks are kept from the origin LV to increase speed. The cache metadata LV holds the accounting information that specifies where data blocks are stored (e.g. on the origin LV or on the cache data LV). Users should be familiar with these LVs if they wish to create the best and most robust cached logical volumes. Cache Terms origin LV OriginLV large slow LV cache data LV CacheDataLV small fast LV for cache pool data cache metadata LV CacheMetaLV small fast LV for cache pool metadata cache pool LV CachePoolLV CacheDataLV + CacheMetaLV cache LV CacheLV OriginLV + CachePoolLV Cache Steps The steps to create a logical volume of cache type are as follows: 0. Create an LV or identify an existing LV to be the origin LV. 1. Create the cache data LV. The size of this LV is the size of the cache and will be reported as the size of the cache pool LV. 2. Create the cache metadata LV. The size of this LV should be 1000 times smaller than the cache data LV with a minimum size of 8MiB. 3. Create the cache pool LV by combining the cache data LV (from step 1) and cache metadata LV (from step 2). When performing this step, behavioral characteristics of the cache pool LV can be set. The name of the cache pool LV takes the name of the cache data LV and the cache data LV and cache metadata LV are renamed to CachePoolLV_cdata and CachePoolLV_cmeta. 4. Create a cache LV by linking the cache pool LV to the origin LV. The user accessible cache LV takes the name of the origin LV, while the origin LV becomes a hidden LV with the name OriginLV_corig. Users can perform this step while the origin LV is in use. The steps above represent the best way to create a cache LV. They provide the most options and have the ability to create the most robust logical volumes. The examples below illustrate how these steps might be used in practice. Cache Commands 0. create OriginLV lvcreate -L LargeSize -n OriginLV VG SlowPVs 1. create CacheDataLV lvcreate -L CacheSize -n CacheDataLV VG FastPVs 2. create CacheMetaLV lvcreate -L MetaSize -n CacheMetaLV VG FastPVs 3. create CachePoolLV lvconvert --type cache-pool --poolmetadata VG/CacheMetaLV VG/CacheDataLV CachePoolLV takes the name of CacheDataLV. CacheDataLV is renamed CachePoolLV_cdata and becomes hidden. CacheMetaLV is renamed CachePoolLV_cmeta and becomes hidden. 4. create CacheLV lvconvert --type cache --cachepool VG/CachePoolLV VG/OriginLV CacheLV takes the name of OriginLV. OriginLV is renamed OriginLV_corig and becomes hidden. Cache Examples Example 1: Creating a simple cache LV. 0. Create the origin LV # lvcreate -L 10G -n lvx vg /dev/slow_dev 1. Create a cache data LV # lvcreate -L 1G -n lvx_cache vg /dev/fast_dev 2. Create a cache metadata LV (~1/1000th size of CacheDataLV or 8MiB) # lvcreate -L 8M -n lvx_cache_meta vg /dev/fast_dev 3. Create a cache pool LV, combining cache data LV and cache metadata LV # lvconvert --type cache-pool --poolmetadata vg/lvx_cache_meta vg/lvx_cache 4. Create a cached LV by combining the cache pool LV and origin LV # lvconvert --type cache --cachepool vg/lvx_cache vg/lvx Example 2: Creating a cache LV with a fault tolerant cache pool LV. 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 that. Note that only steps 1 & 2 change. 0. Create an origin LV we wish to cache # lvcreate -L 10G -n lvx vg /dev/slow_devs 1. Create a 2-way RAID1 cache data LV # lvcreate --type raid1 -m 1 -L 1G -n lvx_cache vg /dev/fast1 /dev/fast2 2. Create a 2-way RAID1 cache metadata LV # lvcreate --type raid1 -m 1 -L 8M -n lvx_cache_meta vg /dev/fast1 /dev/fast2 3. Create a cache pool LV combining cache data LV and cache metadata LV # lvconvert --type cache-pool --poolmetadata vg/lvx_cache_meta vg/lvx_cache 4. Create a cached LV by combining the cache pool LV and origin LV # lvconvert --type cache --cachepool vg/lvx_cache vg/lvx Example 3: Creating a simple cache LV with writethough caching. Some users wish to ensure that any data written will be stored both in the cache pool LV and on the origin LV. The loss of a device asso- ciated with the cache pool LV in this case would not mean the loss of any data. When combining the cache data LV and the cache metadata LV to form the cache pool LV, properties of the cache can be specified - in this case, writethrough vs. writeback. Note that only step 3 is affected in this case. 0. Create an origin LV we wish to cache (yours may already exist) # lvcreate -L 10G -n lvx vg /dev/slow 1. Create a cache data LV # lvcreate -L 1G -n lvx_cache vg /dev/fast 2. Create a cache metadata LV # lvcreate -L 8M -n lvx_cache_meta vg /dev/fast 3. Create a cache pool LV specifying cache mode "writethrough" # lvconvert --type cache-pool --poolmetadata vg/lvx_cache_meta --cachemode writethrough vg/lvx_cache 4. Create a cache LV by combining the cache pool LV and origin LV # lvconvert --type cache --cachepool vg/lvx_cache vg/lvx Removing Cache Logical Volumes If you wish to remove all logical volumes associated with a cache LV, you must remove both top-level, user-visible devices. The cache metadata LV and cache data LV cannot be removed directly. If only the cache pool LV is specfied for removal, any cached blocks not yet on the origin LV will be flush, the cache pool LV will be removed, and the now un-cached origin LV will remain. If the user specifies a cache LV for removal, then the origin LV is removed and only the cache pool LV will remain. The cache pool LV can then be used to create another cache LV with a different origin LV if desired. When users intend to remove all logical volumes associated with a cache LV, it is generally better to start with the origin LV and then remove the cache pool LV. If the operations are performed in the reverse order, the user will have to wait for the contents of the cache pool LV to be flushed before the origin LV is removed. This could take some time. DIAGNOSTICS
All tools return a status code of zero on success or non-zero on failure. FILES
/etc/lvm/lvm.conf $HOME/.lvm_history SEE ALSO
lvm.conf(5), clvmd(8), lvchange(8), lvcreate(8), lvdisplay(8), lvextend(8), lvmchange(8), lvmdiskscan(8), lvreduce(8), lvremove(8), lvre- name(8), lvresize(8), lvs(8), lvscan(8), pvchange(8), pvck(8), pvcreate(8), pvdisplay(8), pvmove(8), pvremove(8), pvs(8), pvscan(8), vgcfg- backup(8), vgchange(8), vgck(8), vgconvert(8), vgcreate(8), vgdisplay(8), vgextend(8), vgimport(8), vgimportclone(8), vgmerge(8), vgmkn- odes(8), vgreduce(8), vgremove(8), vgrename(8), vgs(8), vgscan(8), vgsplit(8), readline(3) Sistina Software UK LVM TOOLS 2.02.105(2)-RHEL7 (2014-03-26) LVM(8)

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