HP Veritas Volume Manager 5.0 -UX 11i v3 manual Creating instant snapshots

voliomem_maxpool_sz

320Administering volume snapshots

Creating instant snapshots

You can create instant snapshots of volume sets by replacing volume names with volume set names in the vxsnap command. For more information, see “Creating instant snapshots of volume sets” on page 334.

Note: When using the vxsnap prepare or vxassist make commands to make a volume ready for instant snapshot operations, if the specified region size exceeds half the value of the tunable voliomem_maxpool_sz (see “voliomem_maxpool_sz” on page 483), the operation succeeds but gives a

warning such as the following (for a system whereis set to 12MB):

VxVM vxassist WARNING V-5-1-0 Specified regionsize is larger than the limit on the system (voliomem_maxpool_sz/2=6144k).

If this message is displayed, vxsnap make, refresh and restore operations on such volumes fail as they might potentially hang the system. Such volumes can be used only for break-off snapshot operations using the reattach and make operations.

To make the volumes usable for instant snapshot operations, use vxsnap unprepare on the volume, and then use vxsnap prepare to re-prepare the volume with a region size that is less than half the size of voliomem_maxpool_sz (in this example, 1MB):

#vxsnap -g mydg -f unprepare vol1

#vxsnap -g mydg prepare vol1 regionsize=1M

To create and manage a snapshot of a volume with the vxsnap command, follow the procedure in “Preparing to create instant and break-off snapshots” on page 321, and then use one of the procedures described in the following sections:

■“Creating and managing space-optimized instant snapshots” on page 324

■“Creating and managing full-sized instant snapshots” on page 327

■“Creating and managing third-mirror break-off snapshots” on page 329

■“Creating and managing linked break-off snapshot volumes” on page 331