Veritas Volume Manager 4.1 Administrator's Guide (HP-UX 11i v3, February 2007)

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Administering Volume Snapshots

Note The FastResync feature is not supported by VxVM 4.1 on the HP-UX 11i v3

platform.

VERITAS Volume Manager (VxVM) provides the capability for taking an image of a

volume at a given point in time. Such an image is referred to as a volume snapshot. You can

also take a snapshot of a volume set as described in “Creating Instant Snapshots of

Vol ume S ets” on page 284.

Volume snapshots allow you to make backup copies of your volumes online with minimal

interruption to users. You can then use the backup copies to restore data that has been lost

due to disk failure, software errors or human mistakes, or to create replica volumes for the

purposes of report generation, application development, or testing.

For an introduction to the volume snapshot feature, see “Volume Snap shot s” on page 45.

More detailed descriptions of each type of volume snapshot and the operations that you

can perform on them may be found in the following sections:

◆ “Traditional Third-Mirror Break-Off Snapshots” on page 263

◆ “Full-Sized Instant Snapshots” on page 265

◆ “Space-Optimized Instant Snapshots” on page 267

◆ “Emulation of Third-Mirror Break-Off Snapshots” on page 268

◆ “Cascaded Snapshots” on page 269

◆ “Creating Multiple Snapshots” on page 273

◆ “Restoring the Original Volume from a Snapshot” on page 274

Note A volume snapshot represents the data that exists in a volume at a given point in

time. As such, VxVM does not have any knowledge of data that is cached by the

overlying file system, or by applications such as databases that have files open in

the file system. If the fsgen volume usage type is set on a volume that contains a

VERITAS File System (VxFS), intent logging of the file system metadata ensures the

internal consistency of the file system that is backed up. For other file system types,

depending on the intent logging capabilities of the file system, there may

potentially be inconsistencies between data in memory and in the snapshot image.