HP D5970A - NetServer - LCII Configuration Manual page 38

Chapter 4

Plan Hot Spares (Optional)
On Worksheet A, 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 HP NetRAID 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, 3, 5,
10, 30, 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.
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.

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
Planning