Using CLI Commands LVM
When sizes are required in a command line argument, units can always be specified explicitly. If you do not specify a unit, then a default is assumed, usually KB or MB. LVM CLI commands do not accept fractions.
When specifying units in a command line argument, LVM is case-insensitive; specifying M or m is equivalent, for example, and powers of 2 (multiples of 1024) are used. However, when specifying the –units argument in a command, lower-case indicates that units are in multiples of 1024 while upper-case indicates that units are in multiples of 1000.
All LVM commands accept a -v argument, which can be entered multiple times to increase the output verbosity. For example, the following examples shows the default output of the lvcreate command.
lvcreate -L 50MB new_vg
lvcreate command with the -v argument.
lvcreate -v -L 50MB new_vg
Tags: CLI, Commands, LVM
Growing a File System on a Logical Volume
To grow a file system on a logical volume, perform the following steps:
1. Make a new physical volume.
2. Extend the volume group that contains the logical volume with the file system you are growing to include the new physical volume.
3. Extend the logical volume to include the new physical volume.
4. Grow the file system.
*If you have sufficient unallocated space in the volume group, you can use that space to extend the logical volume instead of performing steps 1 and 2.
Tags: file, Growing, Logical, System, Volume
The LVM Configuration Files
LVM supports multiple configuration files. At system startup, the lvm.conf configuration file is loaded from the directory specified by the environment variable LVM_SYSTEM_DIR, which is set to /etc/lvm by default.
The lvm.conf file can specify additional configuration files to load. Settings in later files override settings from earlier ones. To display the settings in use after loading all the configuration files, execute the lvm dumpconfig command.
The following files are used for LVM configuration:
/etc/lvm/lvm.conf
Central configuration file read by the tools.
–
/etc/lvm/lvm_hosttag.conf
For each host tag, an extra configuration file is read if it exists: lvm_hosttag.conf.
Tags: configuration, Files, LVM
Snapshot Volumes
The LVM snapshot feature provides the ability to create virtual images of a device at a particular instant without causing a service interruption. When a change is made to the original device (the origin) after a snapshot is taken, the snapshot feature makes a copy of the changed data area as it was prior to the change so that it can reconstruct the state of the device.
LVM snapshots are not supported across the nodes in a cluster. You cannot create a snapshot
volume in a clustered volume group.
LVM snapshots are not supported for LVM mirrored logical volumes.
Snapshot copies of a file system are virtual copies, not actual media backup for a file system.
Snapshots do not provide a substitute for a backup procedure.
Tags: Snapshot, Volumes
Striped Logical Volumes
When you write data to an LVM logical volume, the file system lays the data out across the underlying physical volumes. You can control the way the data is written to the physical volumes by creating a striped logical volume.
For large sequential reads and writes, this can improve the efficiency of the data I/O.Striping enhances performance by writing data to a predetermined number of physical volumes in round-robin fashion. With striping, I/O can be done in parallel. In some situations, this can result in near-linear performance gain for each additional physical volume in the stripe.
Tags: Logical, Striped, Volumes
