Chapter 2. Hardware configuration 35
Depending on the number of installed disks and the number of required host connections,
several I/O enclosures might not contain any adapters.
DAs are called
DA pairs, because DAs are always installed in quantities of two (one DA is
attached to each processor complex). The members of a DA pair are split across two I/O
enclosures for redundancy. The number of installed disk devices determines the number of
required DAs. In any I/O enclosure, the number of individual DAs installed can be zero, one,
or two.
2.3.2 PCIe infrastructure
The DS8800 processor complex and the DS8700 processor complex use a PCI Express
(PCIe) infrastructure to access the I/O enclosures. This infrastructure greatly improves
performance ...