Compaq HSZ80 manual 14Creating Storagesets, First Mirrorset Members on Different Buses

3–14Creating Storagesets

■If you are using more than one mirrorset in your subsystem, you should put the first member of each mirrorset on different buses as shown in Figure 3–6.The first member of a mirrorset is the first disk drive you add.

When a controller receives a request to read data from a mirrorset, it typically accesses the first member of the mirrorset. Read access depends upon the read source switches (see “Read Source,” page 3–46).If you have several mirrorsets in your subsystem and their first members are on the same bus, that bus will be forced to handle the majority of read traffic to your mirrorsets. When a controller receives a request to write data to a mirrorset, it accesses and writes to all mem- bers.

First member

First member of Mirrorset 2 of Mirrorset 1

CXO5506A

Figure 3–6. First Mirrorset Members on Different Buses

To avoid an I/O bottleneck on one bus, you can simply put the first members on different buses. Additionally, you can set the read-source switch to Round Robin. See “Read Source,” page 3–46,for more information about this switch.

■Place mirrorsets and RAIDsets on different ports to minimize risk in the event of a single port bus failure.

■Mirrorset units are set to WRITEBACK_CACHE by default, which increases a unit’s performance.