Multipath I/O for fibre channel disks

Understanding Multipath I/O

The Multipath I/O feature for fibre channel disks enables you to connect each disk on a single filer to two different host adapters. As a result, there are two access paths to each disk. One path is designated primary and the other secondary. If the primary path to the disk becomes unavailable, the secondary path is automatically used to access the disk.

Advantages of Multipath I/O

By providing redundant paths to the same disk on a single filer, the Multipath I/O feature provides the following advantages:

Overall reliability and uptime of the storage subsystem of the filer is increased.
Disk availability is higher.
Storage subsystem hardware can be maintained with no downtime.
When a primary host adapter is brought down, all traffic moves from that host adapter to the secondary host adapter. As a result, you can perform maintenance tasks, such as replacing a malfunctioning LRC module or cables connecting that host adapter to the disk shelves, without affecting the storage subsystem service.

Requirements to enable Multipath I/O on the filer

The Multipath I/O feature is enabled automatically if your filer meets the following requirements:

It has a 2200 or 2212 host adapter installed in the appropriate slot. Although the 2200 and 2212 host adapters can co-exist with the 2100 and 2000 adapters on a filer, Multipath I/O is supported only on the 2200 and 2212 host adapters.
As of Data ONTAP 6.1, F740, F760, and all F8XX series platforms support the 2200 and 2212 host adapters.

To determine the slot number where a host adapter can be installed in your filer, see the System Configuration Guide at http://now.netapp.com.
It is running the Open Firmware (OFW) version 2.8. You can download the OFW for your filer from http://now.netapp.com.
It is not connected to an FC7 disk shelf (in a back-to-back connection or in a FC-AL) or to any other disk shelf that contains 9-GB disks. The Multipath I/O feature is not supported for 9-GB disks and FC7 disk shelves.
It is not part of a cluster. Multipath I/O setup and clustering setup both require the A and B ports of the disk shelves. Therefore, it is not possible to have both features enabled at the same time.
It has all hardware connections set up for Multipath I/O as specified in the corresponding Fibre Channel StorageShelf guide.

Example of Multipath I/O setup

The following figure illustrates an example of Multipath I/O setup on a filer. The filer has dual-port host adapters installed in slot 7 and slot 8. The host adapter ports connect to the disk shelf ports as shown.

This setup uses two dual-port host adapters to connect to two disk shelf loops, thus preventing the host adapters from being the single points of failure. Although it is not necessary to have a dual-port host adapter to set up Multipath I/O, it is recommended because using dual-port adapters conserves PCI slots.