lvm.7 (2011 03)
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lvm(7) lvm(7)
• Extent size is now a required parameter. For volume groups version 1.0, the default extent size
is 4MB. For volume groups version 2.0 or higher, extent size must be specified.
Volume group versions 2.0 and 2.1 do not support root, boot, swap, or dump. Volume group versions 2.2
and higher do support root, boot, swap, and dump.
Volume groups version 2.0 or higher do not support spare physical volumes.
The maximum number of 1.0 version volume groups per system is 256. The maximum number of 2.0 ver-
sion volume groups per system is 512. The maximum combined 2.0, 2.1, and 2.2 volume groups is 2048.
The vgversion (1M) command allows the migration between any two supported volume group versions,
with the exception of moving back to version 1.0.
Extent Sizing for Volume Group Version 2.0 and Higher
In volume groups version 1.0, LVM metadata is required to fit into a single physical extent. If large
values for maximum physical volumes, logical volumes, and extents per physical volume were chosen,
then a large extent size is required.
In volume groups version 2.0 and higher, metadata is not restricted to an extent. There is an implemen-
tation limit to the number of extents in a volume group (see lvmadm(1M)), so the larger the extent size
the larger the maximum volume group size which can be supported. The amount of space taken up on
each physical volume by LVM metadata is dependent on the physical extent size and the maximum
volume group size specified when the volume group is created. LVM metadata for volume groups version
2.0 and higher may consume more space than on volume groups version 1.0.
The
vgcreate command has a new option (-E) which will show the relationship between extent size
and maximum volume group size.
A smaller extent size allows finer granularity in assigning space to logical volumes. It also means that
smaller blocks of data are marked stale when IOs to a mirror copy fail. For small logical and physical
volumes, a smaller extent size may result in less wasted space.
Since there are limits to the number of extents in a logical or physical volume, a small extent size will
limit the total size of a logical or physical volume. Conversely a larger extent size allows creation of
larger logical volumes and use of larger physical volumes.
Auto Boot Disk Migration
This feature is intended to allow users to configure how LVM handles situations where the physical loca-
tion of the boot disk changes between reboots. This situation can occur during hardware configuration
changes or if boot disk images are cloned. In those situations, Auto Migration of Boot Disk will automati-
cally update stale configuration entries for the root volume group in LVM configuration files
(
/etc/lvmtab or /etc/lvmtab_p
) and the Boot Data Reserved Areas for each bootable physical
volume in the root volume group. The configuration files are synchronized with the information from the
kernel at the time of boot.
The Auto Boot Disk Migration feature (defined by the AUTO_BOOT_MIGRATE flag in the
/etc/lvmrc
file) is turned on by default on the system. When the feature is turned on, any mismatch between the
/etc/lvmtab or /etc/lvmtab_p entries and the on-disk metadata structures for the root volume
group in the kernel will be automatically fixed during the boot process.
The Auto Boot Disk Migration feature can be turned off by editing the
/etc/lvmrc file and setting the
flag AUTO_BOOT_MIGRATE to 0. In those situations, users need to check the syslog file post boot
activity and follow the instructions logged to the file, if any.
Snapshots for Volume Group Version 2.2 and Higher
A snapshot represents a point-in-time image of a logical volume. Multiple snapshots can be created off a
single LVM logical volume.
LVM snapshots let you do the following:
• Use snapshots to back up data on the logical volume without splitting the logical volume. This
reduces the space requirement.
• Create snapshots faster than manually copying over multiple point-in-time copies of the logical
volume.
• Create multiple snapshots of a logical volume. This enables you to have images of the logical volume
for multiple point in time without allocating space equivalent to the entire size of the logical volume
per copy.
HP-UX 11i Version 3: March 2011 − 3 − Hewlett-Packard Company 3