IBM Advanced SerialRAID Adapters SA33-3285-02, User Manual

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Pairs Of Adapter Connectors in the Loop – Mainly Shared Data
The following sequence enables you to determine the best relationship between the
disk drives and the adapter, or adapters, on an SSA loop that contains two or more
pairs of adapter connectors. Most of the disk drives share data access with each other.
1. Determine which data is shared between the pairs of adapter connectors.
2. Assign this data to the disk drives that are equally spaced between the sharing
pairs of adapter connectors.
For example, the loop that is shown in Figure 14 contains 16 disks and four adapters.
In this loop:
v
The pairs of adapter connectors should be spaced between the disk drives.
v
Data that is shared by adapters A and B should be put onto disk drives 1 through 4.
v
Data that is shared by adapters B and C should be put onto disk drives 5 through 8.
Note: For configurations such as that shown here, we recommend that the adapters be
installed in separate using systems. Otherwise, disk drives can become isolated
should both adapters fail, or be held reset, in one of the using systems. See
“One Loop with Two Adapters in One Using System” on page 11 and “One Loop
with Two Adapters in Each of Two Using Systems” on page 12 for more
information.
If two using systems are switched off, disk drives can become isolated if the
SSA subsystem does not have bypass cards (see “Bypass Note” on page 12). If
more than one using system is rebooted at the same time, disk drives can
become isolated while the boot is running.
Disk
1
Disk
2
Disk
3
Disk
4
Disk
5
Disk
6
Disk
7
Disk
8
Disk
9
Disk
10
Disk
11
Disk
12
Disk
13
Disk
14
Disk
15
Disk
16
Adapter B
Adapter D
Adapter
A
Adapter
C
Figure 14. Pairs of Connectors in the Loop – Mainly Shared Data
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