Rules For The Physical Relationship Between Disk Drives And Adapters; One Pair Of Adapter Connectors In The Loop - IBM Advanced SerialRAID Adapters SA33-3285-02 User Manual

Rules for the Physical Relationship between Disk Drives and Adapters

The physical relationship between the disk drives and the adapters in an SSA loop can
affect the performance of the subsystem. The following rules help you to get best
performance from your subsystem.

One Pair of Adapter Connectors in the Loop

The following sequence enables you to determine the best relationship between the
disk drives and the adapter on an SSA loop that contains only one pair of adapter
connectors.
1. Determine which data is accessed most frequently.
2. Assign that data to those disks drives that are farthest (round the loop) from the
adapter connectors. By doing this action, you prevent the activity of the busiest disk
drive from obstructing the data path to the other disk drives.
For example, the loop that is shown in Figure 12 contains 16 disk drives, and the
adapter connectors are between disk drives 1 and 16. The most-frequently-accessed
data, therefore, should be on disk drives 8 and 9.
Figure 12. One Pair of Connectors in the Loop
24
User's Guide and Maintenance Information
Disk Disk Disk
1 2 3
Disk Disk Disk
16 15 14
Disk Disk Disk
4 5 6
Disk Disk Disk
13 12 11
Disk Disk
7 8
Disk Disk
10 9