HSG80 ACS Solution Software V8.6 for Windows NT and Windows 2000 Installation and Configuration Guide

2–16 HSG80 ACS Solution Software Version 8.6 for Windows NT and Windows 2000 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 2–12.
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 2–13
shows a second example of a Mirrorset.