How VxVM handles hardware clones or snapshots


How VxVM handles hardware clones or snapshots
Prev	How Veritas Volume Manager works	Next

Advanced disk arrays provide methods to create copies of physical volumes (disks or LUNs) from the hardware side.

You can create a hardware snapshot (such as an EMC BCV™ or Hitachi ShadowImage™), a hardware mirror, or a hardware clone. You can also use dd or a similar command to clone the disk content.

If the physical volumes are VxVM disks, using a hardware copy method also copies the configuration data stored in the private region of the VxVM managed disk. The hardware disk copy becomes a duplicate of the original VxVM disk. For VxVM to handle the duplicated disk images correctly, VxVM must distinguish between the original and duplicate disk images.

VxVM detects that a disk is a hardware copy, to ensure that the duplicate disks are not confused with the original disks. This functionality enables the server to import a consistent set of disks. By default, VxVM imports the original physical volume but VxVM also enables you to work with the hardware copies on the same server. VxVM provides special options to import a disk group with the cloned images and make a cloned disk group with a unique identity. With care, you can manage multiple sets of hardware copies, even from the same server.

See Importing a disk group containing hardware cloned disks .

VxVM provides the following functionality to handle hardware copies:

Functionality	Description
Distinguishes between the hardware copy and the original data disk.	VxVM discovers a unique disk identifier (UDID) for each disk from the attributes of the hardware disk and stores this value. VxVM compares the discovered UDID to the stored value to detect if a disk is a hardware copy.
Prevents inadvertent sharing over the SAN of an original LUN and one or more of its point-in time copies, mirrors, or replicated copies.	By default, when you import a VxVM disk group, VxVM prevents disks that are identified as clones or copies from being imported. This behavior prevents mistakenly importing a mix of original disks and hardware copies.
Imports the hardware copies as a clone disk group or as a new standard disk group.	If you choose to import the hardware copies of the disks of a VxVM disk group, VxVM identifies the disks as clone disks. You can choose whether to maintain the clone disk status or create a new standard disk group.
Detects the LUN class of the array.	VxVM detects the extended attributes of the array, including the LUN class. The LUN class can help to identify which disks are hardware copies of the VxVM disks.
Provides disk tagging to label and manage sets of disks.	If you create multiple copies of the same set of volumes, you as administrator need to identify which disk copies make up a consistent set of disks. You can use VxVM disk tags to label the sets of disks. For example, if you have multiple point in time snapshots of the same LUN, you can label each with a separate disk tag. Specify the tag to the import operation to import the tagged snapshot LUN.

Prev	Up	Next
Volume sets	Home	How VxVM uses the unique disk identifier (UDID)