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Enabling or disabling read reallocation

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.

About this task

If file fragmentation is a concern for FlexCache volumes, enable read reallocation on the FlexCache origin volume.


  1. Enter the following command:
    vol options vol-name read_realloc [on | space_optimized | off]

    • on enables read reallocation on the volume.
    • space_optimized also enables read reallocation but can be used only on FlexVol volumes or deduplicated volumes.

      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.

    • off disables read reallocation for the volume and is the default setting.

    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:

    vol options vol1 read_realloc space_optimized