A physical reallocation (using the -p option of the reallocate start command) reallocates user data on the physical blocks in the aggregate while preserving the logical block locations within a FlexVol volume. You can perform physical reallocation with FlexVol volumes or files and LUNs within FlexVol volumes.
Physical reallocation might reduce the extra storage requirements in a FlexVol volume when reallocation is run on a volume with Snapshot copies. It might also reduce the amount of data that needs to be transmitted by SnapMirror on its next update after reallocation is performed on a SnapMirror source volume.
Physical reallocation is not supported on FlexVol volumes or on files and LUNs within FlexVol volumes that are in an aggregate created by a version of Data ONTAP earlier than version 7.2.
Physical reallocation is also not supported on RAID0.