14.5.15. Using blockcommit to Shorten a Backing Chain
14.5.15. Using blockcommit to Shorten a Backing Chain This section demonstrates how to use virsh blockcommit to shorten a backing chain. For more background on backing chains, see Section 14.5.18, "Disk Image Management with Live Block Copy" . blockcommit copies data from one part of the chain down into a backing file, allowing you to pivot the rest of the chain in order to bypass the committed portions. For example, suppose this is the current state: Using blockcommit moves the contents of snap2 into snap1, allowing you to delete snap2 from the chain, making backups much quicker. Procedure 14.2. virsh blockcommit Run the following command: The contents of snap2 are moved into snap1, resulting in: base <- snap1 <- active . Snap2 is no longer valid and can be deleted Warning blockcommit will corrupt any file that depends on the -base option (other than files that depend on the -top option, as those files now point to the base). To prevent this, do not commit changes into files shared by more than one guest. The -verbose option allows the progress to be printed on the screen.
base <- snap1 <- snap2 <- active . virsh blockcommit USDdom USDdisk -base snap1 -top snap2 -wait -verbose