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Chapter 4. Virtualization concepts 67
Figure 4-1 Physical layer as the base for virtualization
When you 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 DS6000.
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).
4.2.1 Array sites
An array site is a group of four DDMs. What DDMs make up an array site is pre-determined by
the DS6000, but note, that there is no pre-determined server affinity for array sites. The
DDMs selected for an array site are chosen from the same disk enclosure string (see
Figure 4-2 on page 68). All DDMs in an array site are of the same type (capacity and RPM).
Device Adapter
Server0
Server1
Storage enclosure pair
Switched loop 1
Switches
Device Adapter
Switched loop 2
Inter-server communication