How do “clone volumes” relate to the AFS backup subsystem?
As touched upon in Sections “1.9 And AFS is better […]” and “10.9 Today I accidentally […]”, a clone volume is a complete Read Only copy of the original stored as “volume-name.backup” within AFS. This volume can be mounted within the AFS filesystem tree just like any other, hense ~/.clone. However, unlike an image copy of a volume it doesn’t consume twice the disk space. Instead, during the first clone operation, the original is renamed with a .backup stamp while file system metadata is copied over to a new “original” volume as a set of pointers to the relevant portions of the clone. After cloning, new changes to the original volume are appended as incremental deltas to the master copy. The next clone operation merges the two into a single master copy before starting the cloning procedure on the master yet again. While a volume is being cloned it may defer writes for a short period of time to maintain data consistency between the clone and the master copy, though this usually doesn
