Red Hat CLUSTER SUITE 4.7 - CLUSTER LVM ADMINISTRATORS, Руководство пользователя

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Chapter 4. LVM Administration with CLI Commands
20
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
vgcreate
command if the default is not suitable with the
-s
argument. 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