You can enable read reallocation on traditional volumes and FlexVol volumes to improve subsequent read performance of a file. You can also disable read reallocation.
If file fragmentation is a concern for FlexCache volumes, enable read reallocation on the FlexCache origin volume.
Using space_optimized might be useful if the FlexVol volume has Snapshot copies or is a SnapMirror source. When you use space_optimized, the reallocation update does not result in duplicated Snapshot blocks in the active file system, thus conserving space in the volume. Also, space_optimized might reduce the amount of data that SnapMirror needs to move on the next update. However, space_optimized might also result in degraded Snapshot read performance.
Use space_optimized with deduplicated volumes to rearrange the volume's shared blocks. Read reallocation skips deduplicated data if you set the read_realloc option to on.
space_optimized is not supported if vol-name is in an aggregate that was either created prior to Data ONTAP 7.2 or once reverted to a version earlier than Data ONTAP 7.2.
For more information about the vol options read_realloc command, see the na_vol(1) man page.
The following command enables read reallocation on the vol1 volume: