HP Array Controller HSG V8.7 Software - Manual (Page 88)

3–10 HSG80 User’s Guide
Considerations for Planning a Stripeset
Keep the following points in mind as you plan your stripesets:
n A controller can support up to 45 storagesets, consisting of
stripesets, mirrorsets and RAIDsets (refer to Table 3–1).
n Reporting methods and size limitations prevent certain operating
systems from working with large stripesets. 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 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
initialized (the base member size). Thus, if you combine 9 GB disk
drives with 4 GB disk drives in the same storageset, the 4 GB disk
drive will be the base member size, and you will waste 5 GB of
capacity on each 9 GB member.
If you need high performance and high availability, consider using a
RAIDset, striped mirrorset, or a host-based shadow of a stripeset.
n Striping does not protect against data loss. In fact, because the
failure of one member is equivalent to the failure of the entire
stripeset, the likelihood of losing data is higher for a stripeset than
for a single disk drive.
For example, if the mean time between failures (MTBF) for a single
disk is one hour, then the MTBF for a stripeset that comprises N
such disks is l/N hours. As another example, if a single disk’s
MTBF is 150,000 hours (about 17 years), a stripeset comprising
four of these disks would only have an MTBF of slightly more than
four years.
For this reason, you should avoid using a stripeset to store critical
data. Stripesets are more suitable for storing data that can be
reproduced easily or whose loss does not prevent the system from
supporting its critical mission.
n Evenly distribute the members across the device ports to balance
load and provide multiple paths as shown in the Figure 3–4.