HP Array Controller HSG V8.7 Software - Manual (Page 94)

3–16 HSG80 User’s Guide
The relationship between the chunk size and the average request size
determines if striping maximizes the request rate or the data-transfer
rates. You can set the chunk size or let the controller set it
automatically. See “Chunk Size,” page 3–47, for information about
setting the chunk size.
Considerations for Planning a RAIDset
Keep these points in mind as you plan your RAIDsets:
n A controller can support up to 20 storagesets, consisting of
RAIDsets (refer to Table 3–1).
n Reporting methods and size limitations prevent certain operating
systems from working with large RAIDsets. See the HSG80 Array
Controller ACS Version 8.2G Release Notes or the Getting Started
Guide that came with your platform kit for details about these
restrictions.
n A cache module is required for RAIDsets, but write-back cache
need not be enabled for the RAIDset to function properly.
n Both cache modules must be the same size.
n A RAIDset must include at least 3 disk drives, but no more than 14.
n Evenly distribute the members across the device ports to balance
load and provide multiple paths as shown in Figure 3–4 on page
3–11.
n A storageset should only contain disk drives of the same capacity.
The controller limits the capacity of each member to the capacity of
the smallest member in the storageset when the storageset is
initialzed (the base member size). Thus, if you combine 9 GB disk
drives with 4 GB disk drives in the same storageset, you will waste
5 GB of capacity on each 9 GB member.
n RAIDset units are set to WRITEBACK_CACHE by default which
increases a unit’s performance.
n RAIDsets and mirrorsets on different ports to minimize risk in the
event of a single port bus failure.
n RAIDsets are particularly well-suited for the following:
n Small to medium I/O requests
n Applications requiring high availability