lvm.7 (2010 10)

l
lvm(7) lvm(7)
lvsync Synchronize stale mirrors in logical volumes
vgsync Synchronize stale logical volume mirrors in volume groups
Device Special Files
Starting with HP-UX 11i Version 3, the Mass Storage Stack supports two naming conventions for the dev-
ice special files used to identify devices (see intro (7)). Devices can be represented using:
• Persistent device special files, (
/dev/disk/disk3
), or
• Legacy device special file names, (
/dev/dsk/c0t6d6).
While LVM supports the use of both conventions within the same volume group, the examples shown in
the LVM man pages are all using the legacy device special file convention.
Alternate Links (PVLinks)
In this release of HP-UX, LVM continues to support Alternate Links to a device to allow continued access
to the device, if the primary link fails. This multiple link or multipath solution increases data availabil-
ity, but continues disallowing the simultaneous use of multiple paths.
A new feature was introduced in the Mass Storage Subsystem on HP-UX 11i Version 3 that supports mul-
tiple paths to a device and allows simultaneous access to these paths. The Mass Storage Subsystem will
balance the I/O load across the valid paths. Multipathing is the default unless the
scsimgr command is
used to enable legacy multipathing and also the active path is a legacy device special file. See
scsimgr (1M) for details.
Even though the Mass Storage Subsystem supports 32 multiple paths per physical volume on this version
of HP-UX, LVM does not support more than eight paths to any physical volume. As a result, commands
like
vgcreate and vgextend will not succeed in adding more than eight paths per physical volume.
Additionally, vgimport and vgscan cannot write more than eight paths per physical volume in the
/etc/lvmtab or /etc/lvmtab_p files. If users want to use any specific path other than these eight
paths, then they have to vgreduce one of the alternate paths in the volume group and add that specific
path using vgextend.
It is no longer required or recommended to configure LVM with alternate links. However, it is possible to
maintain the traditional LVM behavior. To do so, both of the following criteria must be met:
• Only the legacy device special file naming convention is used in the volume group configuration.
• The
scsimgr command is used to enable the legacy multipath behavior for each physical volume
in the volume group.
LVM’s Volume Group Versions 1.0, 2.0, 2.1, and 2.2
LVM now has four different volume group version,
1.0, 2.0,
2.1, and 2.2. The original version of
LVM volume group is 1.0. Versions 2.0, 2.1, and 2.2 volume groups allow LVM to increase many of the
limits constraining the size of volume groups, logical volumes, and so on. Version 2.2 volume groups have
the same limits as version 2.1 volume groups. To see a comparison of limits for volume groups version
1.0, 2.0, 2.1, and 2.2, use the
lvmadm command (see lvmadm(1M)).
Version 2.2 volume groups support boot volume groups and snapshot logical volumes (see lvlnboot (1M)
and lvcreate (1M) for more details).
The procedures and command syntax for managing volume groups version 1.0 is unchanged.
To take advantage of the improvements in volume groups version 2.0 or higher, a volume group is
declared to be version 2.0, 2.1, or 2.2 at creation time using the new -V option to the vgcreate com-
mand.
The
vgcreate command will create the volume group directory and group file if they do not already
exist. This is independent of the volume group version.
There are several differences in the procedure for creating a volume group which is to be version 2.0 or
higher.
• The volume group directory and group file will have a different major/minor number combina-
tion. See vgcreate (1M) for details.
• It is no longer necessary to set maximums for physical volumes, logical volumes, or extents per
physical volume. Instead the
vgcreate command expects a maximum size for the volume
group. This size of a volume group is the sum of the user data space on all physical volumes
assigned to the volume group.
2 Hewlett-Packard Company − 2 − HP-UX 11i Version 3: October 2010