HP StorageWorks HSG80 ACS Solution Software V8.8 for HP-UX Installation and Configuration Guide (AA-RV1FA-TE, March 2005)

Planning Storage Configurations
84 HSG80 ACS Solution Software V8.8 for HP-UX Installation and Configuration Guide
■ 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 l
hour, then the MTBF for a stripeset that comprises N such disks is l/N hours.
As another example, if the MTBF of a a single disk is 150,000 hours (about
17 years), a stripeset comprising four of these disks would only have an
MTBF of slightly more than 4 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.
■ Evenly distribute the members across the device ports to balance the load and
provide multiple paths.
■ Stripesets may contain between two and 24 members.
■ If you plan to use mirror members to replace failing drives, then create the
original stripeset as a stripeset of 1-member mirrorsets.
■ Stripesets are well-suited for the following applications:
— Storing program image libraries or run-time libraries for rapid loading.
— Storing large tables or other structures of read-only data for rapid
application access.
— Collecting data from external sources at very high data transfer rates.
■ Stripesets are not well-suited for the following applications:
— A storage solution for data that cannot be easily reproduced or for data
that must be available for system operation.
— Applications that make requests for small amounts of sequentially located
data.
— Applications that make synchronous random requests for small amounts
of data.
Spread the member drives as evenly as possible across the six I/O device ports.
Mirrorset Planning Considerations
Mirrorsets (RAID 1) use redundancy to ensure availability, as illustrated in
Figure 26. For each primary disk drive, there is at least one mirror disk drive.
Thus, if a primary disk drive fails, its mirror drive immediately provides an exact
copy of the data. Figure 27 shows a second example of a mirrorset.