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 for accessing 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, subject to the following restrictions:

Only the F740, F760, F8XX, and FAS900 series filer platforms support Multipath I/O.
Note
None of the NearStore appliance platforms (R100 or R150) support Multipath I/O.
Only the 2200 (P/N X2040B) or 2212 (X2044A) (2044B and X2050A) host adapter installed in the appropriate slot support Multipath I/O.
Although the 2200 and 2212 host adapters can co-exist with older (2100 and 2000) adapters on a filer, Multipath I/O is not supported one the older models.

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.
FC7 and FC8 disk shelves do not support Multipath I/O.
FC9 and DS14 disk shelves must have 2 LRCs to support Multipath I/O.
Older 9-GB disks (ST19171FC) and older 18-GB disks (ST118202FC) do not support Multipath I/O.
Filers configured in clusters (that are not Fabric Metroclusters) do not support Multipath I/O. 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 simultaneously.
Hardware connections must be 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, Network Appliance recommends this setup because using dual-port adapters conserves PCI slots.