IBM DS6000 Series ユーザーズマニュアル

Chapter 11. Performance considerations 

Note that each Fibre Channel switch in the disk subsystems from here on connects to the 
next pair of Fibre Channel switches through its two remaining ports. This is similar to 
inter-switch links between Fibre Channel switches.

Through the affinity of extent pools to servers, the DA in a server is used to drive the I/O to the 
disk drives in the host extent pools owned by its server.

When creating volumes in extent pools, these volumes get an affinity to a certain server 
through the extent pool affinity to a server (see Chapter 4, “Virtualization concepts” on 
page 65). This suggests even distribution of volumes across all ranks in the disk subsystems 
and all loops to balance the workload. Although each HA port can reach any volume in the 
disk subsystem, Figure 11-8 indicates also a server affinity to its local HA and its Fibre 
Channel ports. This introduces the concept of a preferred path. When a volume has an 
affinity, for example, to server 0, and is accessed through a port in the HA of server 0, then 
the I/O is locally processed. When this volume is accessed through the HA of the other 
server, in this example from server 1, then the I/O is routed to the server which owns the 
extent pool, which here is server 0. 

Figure 11-9 on page 230 shows a simplified view of the basic DS6000 structure and how it 
accounts for scalability.

Fibre Channel switch

Fibre Channel switch

Fibre Channel switch

Fibre Channel switch

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