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File placement policies and extending files

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.