After reallocation is enabled on your storage system, you define a reallocation scan for the LUN, file, or volume on which you want to perform a reallocation scan.
- On the storage system’s command line, enter the following command:
reallocate start [-t threshold] [-n] [-o] [-p] [-u] [-i interval] pathname
- -t threshold is a number between 3 (layout is moderately optimal) and 10 (layout is not optimal). The default is 4.
A scan checks the block layout of a LUN, file, or volume before reallocating blocks. If the current layout is below the threshold, the scan does not reallocate blocks in the LUN, file, or volume. If the current layout is equal to or above the threshold, the scan reallocates blocks in the LUN, file, or volume.
Note: Because Data ONTAP also includes “hot spots” in its calculation of whether to start a LUN, file, or volume reallocation, the system might start a reallocation when the average optimization is better than the threshold but a small percentage of the total data is very poorly optimized.
- -n reallocates blocks in the LUN, file, or volume without checking its layout.
- -o runs the job once and then automatically removes it from the system.
- -p reallocates user data on the physical blocks in the aggregate while preserving the logical block locations within a FlexVol volume. You cannot use the -p option with the -u option.
This option also reallocates the shared blocks in a deduplicated volume. Reallocation scans skip deduplicated data if you do not specify the -p option. You can use this option only with FlexVol volumes, with files and LUNs within FlexVol volumes, or with deduplicated volumes.
Do not use -p when you start a reallocation scan on a compressed volume. Starting a reallocation scan on a compressed volume using -p does not optimize the layout of a volume.
- -u duplicates blocks that are shared between files by deduplication. Duplicating the blocks removes the sharing. This option can help remove fragmentation; however, because blocks are duplicated, it can result in increased disk usage, especially for
full reallocation. You cannot use the -u option with the -p option.
- -i interval is the interval, in hours, minutes, or days, at which the scan is performed.
The default interval is 24 hours. You specify the interval as follows:
[m | h | d]
For example, 30m is a 30-minute interval.
The countdown to the next scan begins only after the first scan is complete. For example, if the interval is 24 hours and a scan starts at midnight and lasts for an hour, the next scan begins at 1:00 a.m. the next day—24 hours after the first scan is completed.
- pathname is the path to the LUN, file, or volume on which you want to perform a reallocation scan.
The following commands create a new LUN and a normal reallocation scan that runs every 24 hours:
lun create -s 100g /vol/vol2/lun0
reallocate start /vol/vol2/lun0