This read-only integer reports the size of a RAIDset in megabytes, calculated using 2^20 bytes per megabyte rather than the 1,000,000 some drive vendors use. An administrator uses it to track available capacity across RAIDsets and to reconcile it against the advertised size when validating storage inventory. Noticing this reported size is smaller than a drive vendor's advertised capacity is expected due to the differing megabyte definitions, not a fault.