680 Implementing the IBM Storwize V7000 with IBM Spectrum Virtualize V8.2.1
A chain consists of a set of enclosures that are correctly interconnected (Figure 13-5). Chain 
1 of an I/O group is connected to SAS port 1 of both node canisters. Chain 2 is connected to 
SAS port 2. This configuration means that chain 2 includes the SAS expander and drives of 
the control enclosure.
Figure 13-5   SAS cabling with numbering of enclosures
At system initialization, when devices are added to or removed from strands, IBM Storwize 
V7000 performs a discovery process to update the state of the drive and enclosure objects.
13.1.5  Power
All enclosures accommodate two power supply units (PSUs) for normal operation. A single 
PSU can supply the entire enclosure for redundancy. For this reason, it is highly advised to 
supply AC power to each PSU from different Power Distribution Units (PDUs).
There is a power switch on the power supply and indicator LEDs. The switch must be on for 
the PSU to be operational. If the power switch is turned off, the PSU stops providing power to 
the system. 
For control enclosure PSUs, the battery integrated in the node canister continues to supply 
power to the node. A fully charged battery is able to perform two fire hose dumps. It supports 
the power outage for 5 seconds before initiating safety procedures.