HP P3410A HP NetRAID 1M/2M Installation & Configuration - Page 40

Chapter 4 Planning Plan Hot Spares (Optional) ! On Worksheet A for each adapter, log any hot spare disk modules and indicate whether each is global or dedicated to a particular array. A hot spare is a powered-on, stand-by disk that is ready for use should another disk fail. When a disk fails, the disk array controller's firmware can automatically rebuild the data from the failed disk onto the hot spare. Unless a rebuild occurs, a hot spare does not contain user data. When planning hot spares, keep these considerations in mind: • Hot spares are useful only for logical drives with RAID levels of 1, 5, 10, or 50. • Hot spares cannot rebuild logical drives of RAID 0, because this RAID level does not provide a means of recovering data. • A dedicated hot spare is assigned to a specific array. Only one hot spare can be dedicated to each individual array. • Global hot spares stand ready to rebuild any physical drive for any array with redundancy controlled by the adapter. • A hot spare does not count toward the usable capacity of any array. • A hot spare must have capacity equal to or greater than the capacity of the physical drive it would replace. • An adapter can support up to eight hot spares. Decide the Rebuild Rate ! During a rebuild, the contents of a complete physical drive is rewritten. Normal operations can go on during a rebuild, but performance may be degraded. The Rebuild Rate controls the rate at which a rebuild is done by specifying what percentage of IOP resources will be dedicated to rebuilding the data on a failed physical drive. A high Rebuild Rate (over 50%) speeds up the rebuild, but slows system performance. A low Rebuild Rate (under 50%) slows the rebuild process, but speeds up system performance. The default is 50%. RAID 0 data cannot be rebuilt because it has no redundancy. Log the Rebuild Rate on Worksheet A. 32