A measure-only reallocation scan is similar to a normal reallocation scan except that only the check phase is performed. It allows the optimization of the LUN, file, or volume to be tracked over time or measured ad-hoc.
A measure-only reallocation scan checks the layout of a LUN, file, or volume. If the layout measurement becomes less optimal than the threshold (specified by the -t threshold option), or if a portion of the data is very poorly optimized, the log message advises you to consider performing a LUN, file, or volume reallocation (using the reallocate start command) to optimize the layout.
For scheduled measure-only reallocation scans, the optimization of the last completed check is saved and may be viewed at any time by using reallocate status.
Additional information about the layout of the LUN, file, or volume is logged if you use the -l logfile option.
If logfile is specified, information about the layout is recorded in the file.
A measure-only reallocation scan runs periodically at a system-defined interval, but depending on the system configuration and write/read workload, you can change the job interval with the -i option. You specify the interval as follows:
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.
The following command syntax measures the optimization of the dblun LUN once and records detailed information about the measurement in the measure_log_dblun log:
After a measure-only reallocation scan, the optimization information is logged via EMS in the system log files.