The Multipath I/O feature for Fibre Channel disks enables you to create two paths, a primary path and a secondary path, from a single storage system to a disk loop. You can use this feature with or without SyncMirror.
Although it is not necessary to have a dual-port disk host adapter to set up Multipath I/O, you should use two dual-port host adapters to connect to two disk shelf loops, thus preventing either host adapter from being a single point of failure. In addition, using dual-port host adapters conserves Peripheral Component Interconnect (PCI) slots.
If your environment requires additional fault tolerance, you can use Multipath I/O with SyncMirror and configure it with four separate host adapters, connecting one path from each host adapter to one channel of a disk shelf. With this configuration, not only is each path supported by a separate host adapter, but each host adapter is on a separate bus. If there is a bus failure, or a host adapter failure, only one path is lost.
By providing redundant paths to the same disk on a single storage system, the Multipath I/O feature offers the following advantages:
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 Loop Resiliency Circuit (LRC) module or cables connecting that host adapter to the disk shelves, without affecting the storage subsystem service.
The Multipath I/O feature is enabled automatically, subject to the following restrictions:
Note
None of the NearStore storage systems (R100, R150, or R200 series) support Multipath I/O.
Note
Although the 2200 and 2212 host adapters can co-exist with older (2100 and 2000) adapters on a storage system, Multipath I/O is not supported on older storage systems.
To determine the slot number where a host adapter can be installed in your storage system, see the System Configuration Guide at the NOW site (http://now.netapp.com/).
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.
Note
Storage systems configured in a standard (CFO) cluster do not support Multipath I/O.
Multipath I/O supports the following configurations:
Configure a single storage system for Multipath I/O without SyncMirror by connecting a primary path from one host adapter to one disk loop and a secondary path from another host adapter to that disk loop, as shown in the following illustration. To display the paths using the storage show disk -p command, see Example 1.
If your storage system does not support software-based disk ownership, you need to know which slots the adapters are in because that is what pool ownership is determined by. For example, with the FAS900 series, slots 1 through 7 own Pool0, and slots 8 through 11 own Pool1. In this case, you should configure the system to have a primary path and a secondary path connected from one adapter to the first disk loop and a primary and a secondary path from the other adapter to the second disk loop, as shown in the following illustration. To display the paths using the storage show disk -p command, see Example 2.
If your storage system supports software-based disk ownership, you should configure the system to have a primary path and a secondary path from two different adapters to the first disk loop and a primary and a secondary path from the two adapters to the second disk loop, as shown in the following illustration. To display the paths using the storage show disk -p command, see Example 3.
If you want to provide the highest level of availability, you can configure Multipath I/O with SyncMirror using four separate adapters, one for each disk shelf. For the latest information about which slots to use for adapters in your specific storage system, see the System Configuration Guide.
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Part No. 210-01085_B0
File: 3disk8.htm
Last updated: 01-Dec-2005 16:51:24