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86 DS8000 Series: Concepts and Architecture
Figure 5-2 Physical layer as the base for virtualization
Figure 5-2 shows the physical layer on which virtualization is based.
Compare this with the ESS design, where there was a real loop and having an 8-pack close
to a device adapter was an advantage. This is no longer relevant for the DS8000. Because of
the switching design, each drive is in close reach of the device adapter, apart from a few
more hops through the Fibre Channel switches for some drives. So, it is not really a loop, but
a switched FC-AL loop with the FC-AL addressing schema: Arbitrated Loop Physical
Addressing (AL-PA).
5.3.1 Array sites
An array site is a group of eight DDMs. What DDMs make up an array site is pre-determined
by the DS8000, but note, that there is no pre-determined server affinity for array sites. The
DDMs selected for an array site are chosen from two disk enclosures on different loops (see
Figure 5-3 on page 87).
The DDMs in the array site are of the same DDM type, which means the same capacity and
the same speed (RPM).
Server0
Server1
RIO-G
I/O Enclosure
DAHAHA HAHADA
Storage enclosure pair
Switched loop 1
Switches
Switched loop 2
I/O Enclosure
DAHAHA HAHADA