HSG80 ACS Solution Software Version 8.7 for Compaq Tru64 UNIX Installation and Configuration Guide

Planning Storage Configurations
2–22 HSG80 ACS Solution Software Version 8.7 for Compaq Tru64 UNIX Installation and
Configuration Guide
Keep these points in mind when planning mirrorsets
• Data availability with a mirrorset is excellent but comes with a higher cost—you
need twice as many disk drives to satisfy a given capacity requirement. If
availability is your top priority, consider using dual-redundant controllers and
redundant power supplies.
• You can configure up to a maximum of 20 RAID 3/5 mirrorsets per controller or
pair of dual-redundant controllers. Each mirrorset may contain up to 6 members.
Refer to “Configuration Rules for the Controller” on page 2–3, for detailed
information on maximum numbers. 30 RAID 3/5 and RAID 1 mirrorsets are
permitted, however, there is limit of no more than 20 RAID 3/5 mirrorsets in such
a configuration.
• Both write-back cache modules must be the same size.
• A mirrorset should only contain disk drives of the same capacity.
• Spread mirrorset members across different device ports (drive bays).
• Mirrorsets are well-suited for the following:
— Any data for which reliability requirements are extremely high
— Data to which high-performance access is required
— Applications for which cost is a secondary issue
• Mirrorsets are not well-suited for the following applications:
— Write-intensive applications (a performance hit of 10 percent will occur)
— Applications for which cost is a primary issue
RAIDset Planning Considerations
RAIDsets (RAID 3/5) are enhanced stripesets—they use striping to increase I/O
performance and distributed-parity data to ensure data availability. Figure 2–9 shows
an example of a RAIDset that uses five members.