Multipathing with Local Storage and FC SANs

Multipathing is a technique that lets you use more than one physical path that transfers data between the host and an external storage device.

In a simple multipathing local storage topology, you can use one ESXi host with two HBAs. The ESXi host connects to a dual-port local storage system through two cables. This configuration ensures fault tolerance if one of the connection elements between the ESXi host and the local storage system fails.

To support path switching with FC SAN, the ESXi host typically has two HBAs available from which the storage array can be reached through one or more switches. Alternatively, the setup can include one HBA and two storage processors so that the HBA can use a different path to reach the disk array.

In FC Multipathing, multiple paths connect each host with the storage device. For example, if HBA1 or the link between HBA1 and the switch fails, HBA2 takes over and provides the connection between the server and the switch. The process of one HBA taking over for another is called HBA failover.

The graphic depicts two hosts, Host 1 and Host 2, which are connected to SP1 and SP2 respectively, through switches. HBA 1 and HBA 2 are on Host 1, while HBA 3 and HBA 4 are on Host 2. HBA 2 is connected to the switch uner Host 1, which HBA 1 is connected to the switch under Host 2. HBA 3 is connected to the switch under Host 1, which HBA4 is connected to the switch under Host 2. SP1 and SP2 are in a storrage array. Both are linked to the two switches. — Figure 1. FC Multipathing

If SP1 or the link between SP1 and the switch breaks, SP2 takes over and provides the connection between the switch and the storage device. This process is called SP failover. ESXi multipathing supports HBA and SP failover.

After you have set up your hardware to support multipathing, you can use the vSphere Web Client or vCLI commands to list and manage paths. You can perform the following tasks.

List path information with vicfg-mpath or esxcli storage core path. See Listing Path Information.
Change path state with vicfg-mpath or esxcli storage core path. See Changing the State of a Path.
Change path policies with ESXCLI. See Set Policy Details for Devices that Use Round Robin.
Mask paths with ESXCLI. See the vSphere Storage documentation.
Manipulate the rules that match paths to multipathing plugins to newly discovered devices with esxcli claimrule. See Managing Claim Rules.
Run or rerun claim rules or unclaim paths. See Managing Claim Rules.
Rescan with vicfg-rescan. See Scanning Storage Adapters.