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EVA controller path information

Table 6 describes the information displayed on the EVA controller Paths tab.

Table 6 EVA controller path information

DescriptionInformation type

Online—All paths are active and available for I/O transactions.

Degraded—One or more paths are offline; however, I/O can continue on the remaining

active paths.

Offline—No paths are available. I/O and disk connectivity is lost.

Status

Pressure—The path with the fewest number of bytes being transferred is selected for

I/O. Pressure load balancing is domain based. The first level of path selection is based

on the domain (adapter channel) with the fewest number of bytes being transferred. If

there are multiple paths to a target on a domain, a second level of selection is used.

Pressure load balancing provides the best (or equal) performance of all load balancing

policies regardless of storage topology.

Queue Depth—The path with the fewest outstanding I/O transactions s is selected for

I/O.

HP recommends that this target-based policy not be used in an environment with mixed

I/O transfers to many devices.

Round Robin—The least-used path is selected for I/O. This target-based policy uses the

configuration's cumulative I/O count for path selection. For example, if an I/O operation

starts and finishes on one path to a dual ported device, the second path is used when

the next I/O operation starts.

A round robin policy exercises all paths when the application queue depth to a target

is 1. In other words, it ensures that all hardware devices are used evenly. The other

policies select the same path repeatedly when the queue depth is 1.

Multiple—Different load balancing policies are set on the LUNs at a lower hierarchal

level than the EVA controller device.

Load Balance

The number of bytes transferred between the system and the EVA controller since the

system was booted.

Transfer Count

The world wide port name (WWPN) of an EVA controller Fibre Channel port. The asso-

ciated status icon displays green for an active path or red if the path is offline.

Target Port

Preferred—The target port is currently managing a vdisk.

Alternate—The target port is currently not managing a vdisk.

Multiple—This controller target port is used as a Preferred path and Alternate path by

different LUNs.

The EVA has a pair of active/active controllers that present all LUNs from each controller’s

Fibre Channel ports. When you create a vdisk, you can specify which EVA controller

will manage the LUN to distribute vdisk I/O workload between the EVA controllers.

For optimal performance, the host adapter driver determines which target port manages

the vdisk and automatically sets the read mode to Preferred. A target port that is not

managing the vdisk is set to Alternate. If a preferred target port fails, I/O reads continue

on the alternate path. If a vdisk changes controllers (for example, if a user changes

presentation, or a managing controller fails or reboots) the EVA notifies the host adapter

and the managing EVA target ports are set to Preferred.

Read Mode

The number of bytes transferred between the system and the EVA controller target port

since the system was booted.

Transferred

Mac OS X Fibre Channel connectivity to the HP StorageWorks Enterprise Virtual Array storage system

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