Server 0

Server enclosure

Server 1

Fibre Channel switch

ooo

16 DDM

Fibre Channel switch

Fibre Channel switch

ooo

16 DDM

Fibre Channel switch

Fibre Channel switch

ooo

16 DDM

Fibre Channel switch

Fibre Channel switch

ooo

16 DDM

Fibre Channel switch

Expansion enclosure

Expansion enclosure

Expansion enclosure

Figure 11-9 DS6000 interconnects to expansion enclosures and scales very well

Figure 11-9outlines how expansion enclosures connect through inter-switch links to the server enclosure. Note the two Fibre Channel loops which are evenly populated as the number of expansion enclosures grow.

11.4 Performance and sizing considerations for open systems

To determine the most optimal DS6000 layout, the I/O performance requirements of the different servers and applications should be defined up front since they will play a large part in dictating both the physical and logical configuration of the disk subsystem. Prior to designing the disk subsystem, the disk space requirements of the application should be well understood.

11.4.1 Workload characteristics

The answers to questions like how many host connections do I need?, how much cache do I need? and the like always depend on the workload requirements (such as, how many I/Os per

second per server, I/Os per second per gigabyte of storage, and so forth).

The information you need, ideally, to conduct detailed modeling includes:

￿Number of I/Os per second

￿I/O density

￿Megabytes per second

￿Relative percentage of reads and writes

￿Random or sequential access characteristics

￿Cache hit ratio

230DS6000 Series: Concepts and Architecture

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IBM DS6000 Series manual Performance and sizing considerations for open systems, Workload characteristics