IBM TotalStorage DS6000 Series: Performance Monitoring and Tuning

Chapter 6. IBM TotalStorage SAN Volume Controller attachment 171

Figure 6-2 Relationship between physical and virtual

6.1.2 SAN Volume Controller multipathing

Each SAN Volume Controller node presents a vDisk to the SAN via multiple paths, usually

four. Since in normal operation two nodes are used to provide redundant paths to the same

storage, this means that depending on zoning, a single host HBA will see up to eight paths to

each LUN presented by the SAN Volume Controller. Because most operating systems are not

able to resolve multiple paths back to a single physical device, IBM provides a multi-pathing

device driver.

The multi-pathing driver supported by the SAN Volume Controller is IBM’s Subsystem Device

Driver (SDD). It manages the multiple paths from the host to the SAN Volume Controller

making use of the preferred paths in a round robin manner before using any non-preferred

path. SDD performs data path failover in the event of a failure within the SAN Volume

Controller, or the host path while also masking out the additional disks that would otherwise

be seen by the hosts due to the redundant paths through the SAN fabric.

Note: The SDD code has been updated to support both the SAN Volume Controller, the

ESS, the DS6000 and the DS8000, and provided the latest version is used, IBM supports

the concurrent connections of a host to both a SAN Volume Controller and “native” storage

environments. Refer to IBM SDD documentation:

Multipath Subsystem Device Driver

User's Guide

, SC30-4096.