In a VxFS file system with an active file placement policy, the placement class on whose volume a file resides is part of its metadata, attached when it is created, and updated when it is relocated. When an application extends a file, VxFS allocates the incremental space on the volume occupied by the file if possible, and on another volume in the same placement class if not. For example, if a file is created on a tier1
volume, and later relocated to a tier2
volume, extensions to the file that occur prior to the relocation have space allocated on a tier1
volume, while those occurring subsequent to the relocation have their space allocated on tier2
volumes. When a file is relocated, all of its allocated space, including that acquired by extension, is relocated, to tier2
volumes in this case.