Storage Area Networks For Dummies®

Chapter 15: Everything You Ever Wanted to Know about Virtualization
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This example is extreme, because rarely are all these solutions used together.
However, using virtualization, each layer in the datacenter can be made more
efficient and simpler to manage.
A single virtualization solution can be deployed at a single layer, or virtualization
solutions can be combined for added functionality. Another example
of virtualization inside a server at the HBA layer is the use of path failover
(sometimes called filter driver) software on the servers in your SAN. The path
failover driver virtualizes (abstracts) the connections (paths) to your storage
array over the SAN fabric and enables your operating system to failover to
the other path if one goes away.
As you can see in Figure 15-5, the path failover driver virtualizes the paths
to the primary disk for this server. The server sees only a single disk even
though two paths exist to the same disk. If one of the paths fails, the driver
simply enables the I/O operations to travel down the surviving path. In this
way, the path failover driver provides a simple virtualization function at the
server or host level. Many path failover software solutions can provide up to
32 paths per LUN to further increase performance.
Path Failover
Driver
Fabric A
Fabric B
Figure 15-5:
Path failover
drivers
provide a
virtual path
to disk.
Primary