HP StorageWorks Virtual Array 7000 Family User and Service Guide (January 2005)

Product Overview 45
Product Overview
Performance Path
The performance path is the most direct path from the host to the data in the
array. It is specified by two separate device files that direct the data either
through Controller 1 or through Controller 2. The performance path is always
the faster path in terms of data transfer rate.
Because the array has two active controllers, the host will typically have two
paths to data, as shown in Figure 17.
■ The primary path is through the controller which owns the LUN being
accessed. That is, the controller that manages the RG the LUN belongs to.
On the VA 7400 and 7410 each LUN is assigned to RG1 or RG2,
managed by controller 1 and controller 2 respectively. When accessing
data on a LUN, the host should send I/Os to the controller which owns the
LUN.
■ The secondary path is through the controller which does not own the LUN
being accessed. In this situation, the non-owning controller must use the
internal N-Way bus to send the I/O to the controller that owns the LUN.
Whenever the secondary path is used, I/O performance is impacted due
to the inter-controller communication required.
System and SAN configuration with the knowledge of the performance path is
a technique to maximize the array performance. For normal workloads this
provides very little performance improvements, but for benchmarking and
highly utilized arrays, this can provide modest performance gains. The biggest
gains can be found with the VA 7100/7400, improvements with the
VA 7110/7410 have reduced the performance gained through performance
path management.
The use of load balancing software in normal workloads, such as HP AutoPath,
can, in many cases, offset any gains in performance by managing the
configuration of the performance path.
VA 7100/7110 Performance Path
In the VA 7100, the performance path is always specified by the device file for
Controller 1. Because the VA 7100 has only one redundancy group, and the
secondary controller is recommended only for failover, the primary controller
is always the most direct path to the data. If Controller 1 fails, the host should
use the secondary path to Controller 2.