Compaq AA-RHGWB-TE manual Planning Your Configuration, To increase You can

•Number of shared SCSI buses and the storage on each shared bus

Using shared SCSI buses increases storage availability. You can connect 32 shared SCSI buses to a cluster member. You can use any combination of KZPSA-BB, KZPBA-CB, or KGPSA-BC/CA host bus adapters.

In addition, RAID array controllers allow you to increase your storage capacity and protect against disk, controller, host bus adapter, and SCSI bus failures. Mirroring data across shared buses provides you with more reliable and available data. You can use Logical Storage Manager (LSM) host-based mirroring for all storage except the clusterwide root (/) file system, the member-specific boot disks, and the swap and quorum disk.

•No single-point-of-failure (NSPOF) TruCluster Server cluster

You can use mirroring and multiple-bus failover with the HSZ70, HSZ80, and HSG80 RAID array controllers to create a NSPOF TruCluster Server cluster (providing the rest of the hardware is installed).

•Tape loaders on a shared SCSI bus

Because of the length of the internal SCSI cables in some tape loaders (up to 3 meters), they cannot be externally terminated with a trilink/terminator combination. Therefore, in general, with the exception of the TL890, TL891, and TL892, tape loaders must be on the end of the shared SCSI bus. See Chapter 8 for information on configuring tape devices on a shared SCSI bus.

•You cannot use Prestoserve in a TruCluster Server cluster to cache I/O operations for any storage device, regardless of whether it is located on a shared bus or a bus local to a given system. Because data in the Prestoserve buffer cache of one member is not accessible to other member systems, TruCluster Server cannot provide correct failover when Prestoserve is being used.

Table 4–1 describes how to maximize performance, availability, and storage capacity in your TruCluster Server hardware configuration. For example, if you want greater application performance without decreasing I/O performance, you can increase the number of member systems or you can set up additional shared storage.

Table 4–1: Planning Your Configuration

To increase:	You can:
Application performance	Increase the number of member systems.
I/O performance	Increase the number of shared buses.
Member system availability	Increase the number of member systems.
Cluster interconnect availability	Use redundant cluster interconnects.

TruCluster Server System Configuration Using UltraSCSI Hardware 4–3