IBM DS8000 manual Host adapters, AAL benefits, DDMs

the array is placed on each loop. If the disk enclosures were fully populated with DDMs, there would be four array sites.

loop 0

Server

0

device

adapter

loop 1

Fibre channel switch 1

2

Array site 0 Array site 1

3

4

loop 0

Server

1

device

adapter

loop 1

There are two separate switches in each enclosure.

Figure 2-15 Array across loop

AAL benefits

AAL is used to increase performance. When the device adapter writes a stripe of data to a RAID-5 array, it sends half of the write to each switched loop. By splitting the workload in this manner, each loop is worked evenly, which improves performance. If RAID-10 is used, two RAID-0 arrays are created. Each loop hosts one RAID-0 array. When servicing read I/O, half of the reads can be sent to each loop, again improving performance by balancing workload across loops.

DDMs

Each DDM is hot plugable and has two indicators. The green indicator shows disk activity while the amber indicator is used with light path diagnostics to allow for easy identification and replacement of a failed DDM.

At present the DS8000 allows the choice of three different DDM types:

￿73 GB, 15K RPM drive

￿146 GB, 10K RPM drive

￿300 GB, 10K RPM drive

2.5Host adapters

The DS8000 supports two types of host adapters: ESCON and Fibre Channel/FICON. It does not support SCSI adapters.

Chapter 2. Components 37