HP Array Controller HSG V8.7 Software - Manual (Page 125)

Creating Storagesets 3–47
Initialize Switches
You can enable the following kinds of switches to affect the format of a
disk drive or storageset:
n Chunk size (for stripesets and RAIDsets only)
n Save configuration
n Destroy/Nodestroy
After you initialize the storageset or disk drive, you cannot change
these switches without reinitializing the storageset or disk drive.
Chunk Size
Specify a chunk size to control the stripesize used for RAIDsets and
stripesets:
n CHUNKSIZE=DEFAULT lets the controller set the chunk size
based on the number of disk drives (d) in a stripeset or RAIDset. If
d < 9 then chunk size = 256. If d > 9 then chunk size = 128.
n CHUNKSIZE=n lets you specify a chunk size in blocks. The
relationship between chunk size and request size determines
whether striping increases the request rate or the data-transfer rate.
See page B–72 for more information on Chunk Size.
Tip While a storageset may be initialized with a user-selected chunk
size, it is recommended that only the default value be used. The default
value is chosen to produce optimal performance for a wide variety of
loads. The use of a chunk size less than 128 blocks (64K) is strongly
discouraged. There are almost no customer loads for which small
chunk sizes are of value and, in almost all cases, selecting a small
chunk size will severely degrade the performance of the storageset and
the controller as a whole. Use of a small chunk size on any storageset
can result in severe degradation of overall system performance.
Increasing the Request Rate
A large chunk size (relative to the average request size) increases the
request rate by allowing multiple disk drives to respond to multiple
requests. If one disk drive contains all of the data for one request, then