24 Implementing the IBM Storwize V7000 with IBM Spectrum Virtualize V8.2.1
2.5.7  HyperSwap
IBM HyperSwap function is a high availability feature that provides dual-site, active-active 
access to a volume. Active-active volumes have a copy in one site and a copy at another site. 
Data that is written to the volume is automatically sent to both copies so that either site can 
provide access to the volume if the other site becomes unavailable. Active-active 
relationships are made between the copies at each site. These relationships automatically 
run and switch direction according to which copy or copies are online and up to date. 
Relationships can be grouped into consistency groups as with Metro Mirror and Global Mirror 
relationships. The consistency groups fail over consistently as a group based on the state of 
all copies in the group. An image that can be used if a disaster occurs is maintained at each 
site. When the system topology is set to HyperSwap, each IBM Storwize V7000 controller and 
hostmap object in the system configuration must have a site attribute set to 1 or 2. 
This site must be the same site as the site of the controllers that provide the managed disks to 
that I/O group. When managed disks are added to storage pools, their site attributes must 
match. This requirement ensures that each copy in the active-active relationship is fully 
independent and is at a distinct site.
2.5.8  Dense expansion drawers
Dense expansion drawers, or dense drawers, are optional disk expansion enclosures that are 
5U rack-mounted. Each chassis features two expansion canisters, two power supplies, two 
expander modules, and a total of four fan modules.
Each Dense Drawer can hold up 92 drives that are positioned in four rows of 14 and another 
three rows of 12 mounted drives assemblies. Two Secondary Expander Modules (SEM) are 
centrally located in the chassis. One SEM addresses 54 drive ports, and the other addresses 
38 drive ports.
The drive slots are numbered 1 - 14, starting from the left rear slot and working from left to 
right, back to front.
Each canister in the Dense Drawer chassis features two SAS ports numbered 1 and 2. The 
use of SAS port1 is mandatory because the expansion enclosure must be attached to an IBM 
Storwize V7000 node or another expansion enclosure. SAS connector 2 is optional because it 
is used to attach to more expansion enclosures.
Each IBM Storwize V7000 can support up to four dense drawers per SAS chain.