LVM Volume Group Quiesce/Resume

Overview

The LVM Quiesce/Resume feature should be used when it is necessary to obtain a

stable image of all the disks in an otherwise active volume group. The feature is

designed to be used with disk array management or backup management tools to

facilitate creating a disk image snapshot copy of the LVM metadata and user data on the

disks in the volume group for backup purposes. Since LVM updates can occur at any

time, LVM accesses to the disks must be quiesced to assure that the disk image will not

be changing while a disk snapshot is in progress.

Disks in an active volume group are routinely updated by LVM

It is important to note that LVM can perform metadata updates at any time, even when

there is no application I/O in progress to the volume group. Any LVM disk that is part

of an activated volume group can be modified by LVM at any time to update LVM

status and configuration information (LVM metadata). Consequently, if a snapshot is

taken without quiescing the volume group the metadata in the backup may not

accurately reflect the status or configuration data in the volume group. Additionally, if

application writes are in progress to a mirrored logical volume, the snapshot could

contain different data in the mirror copies.

Quiescing the volume group provides a stable unchanging disk image

Once the volume group has been quiesced, the disk image for the volume group does

not change. The LVM metadata and application data on the disks remains unchanged.

The logical volume mirrored data in the volume group is consistent. A hardware

snapshot of all the disks can be taken and used as a backup. When the backup volume

group is activated, the user application data and LVM metadata on the disks in the

backup will appear as it was the moment that the volume group was quiesced.

There are other ways to obtain a stable image of application data in a logical

volume

The lvsplit command allows splitting off a copy of a mirrored logical volume within a

volume group. The split copy will remain unchanged and can be used to perform a

backup of the logical volume. It is not necessary to use the Quiesce/Resume feature

with lvsplit). The LVM Volume Group Quiesce/Resume feature is only required to

assist disk array management or backup management tools to create an unchanging

image (snapshot) of all the disks in a volume group (including the LVM metadata).