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You can define allocation policies with a balance allocation order and "chunk" size to files or a file system, known as extent balancing. The chunk size is the maximum size of any extent that files or a file system with this assigned policy can have. The chunk size can only be specified for allocation policies with a balance allocation order.
An extent balancing policy specifies the balance allocation order and a non-zero chunk size. The balance allocation order distributes allocations randomly across the volumes specified in the policy and limits each allocation to a maximum size equal to the specified chunk size.
Extent balancing extends the behavior of policy enforcement by rebalancing extent allocations such that each volume in the policy is as equally used as possible. Policy enforcement handles the following cases:
New volumes are added to the policy, and the extents associated with a file need rebalancing across all volumes, including the new ones.
Volumes are removed from the volume set or from the policy, and the extents for a file residing on a removed volume need to be moved to other volumes in the policy.
An extent balancing policy is assigned to a file and its extents have to be reorganized to meet the chunk size requirements defined in the policy.
The extent balancing policy is intended for balancing data extents belonging to files across volumes defined in the policy. However, there is no restriction imposed in assigning extent balancing policy for metadata.