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Chapter 4. LVM Administration with CLI Commands
4.3.1. Creating Volume Groups
To create a volume group from one or more physical volumes, use the vgcreate command. The
vgcreate command creates a new volume group by name and adds at least one physical volume to
it.
The following command creates a volume group named vg1 that contains physical volumes /dev/
sdd1 and /dev/sde1.
vgcreate vg1 /dev/sdd1 /dev/sde1
When physical volumes are used to create a volume group, its disk space is divided into 4MB extents,
by default. This extent is the minimum amount by which the logical volume may be increased or
decreased in size. Large numbers of extents will have no impact on I/O performance of the logical
volume.
You can specify the extent size with the -s option to the vgcreate command if the default extent size
is not suitable. You can put limits on the number of physical or logical volumes the volume group can
have by using the -p and -l arguments of the vgcreate command.
By default, a volume group allocates physical extents according to common-sense rules such as
not placing parallel stripes on the same physical volume. This is the normal allocation policy.
You can use the --alloc argument of the vgcreate command to specify an allocation policy of
contiguous, anywhere, or cling.
The contiguous policy requires that new extents are adjacent to existing extents. If there are
sufficient free extents to satisfy an allocation request but a normal allocation policy would not use
them, the anywhere allocation policy will, even if that reduces performance by placing two stripes
on the same physical volume. The cling policy places new extents on the same physical volume
as existing extents in the same stripe of the logical volume. These policies can be changed using the
vgchange command.
In general, allocation policies other than normal are required only in special cases where you need to
specify unusual or nonstandard extent allocation.
LVM volume groups and underlying logical volumes are included in the device special file directory
tree in the /dev directory with the following layout:
/dev/vg/lv/
For example, if you create two volume groups myvg1 and myvg2, each with three logical volumes
named lvo1, lvo2, and lvo3, this create six device special files:
/dev/myvg1/lv01
/dev/myvg1/lv02
/dev/myvg1/lv03
/dev/myvg2/lv01
/dev/myvg2/lv02
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