When fibre channel is used to connect a host to storage, multple paths (e.g. cables) can be used to allow the system to load-balanced fibre channel frames over one or more links. This allows a host to transparently handle link failures, and allows your host to keep chugging along when you perform SAN maintenance or a GBIC or SFP fails. To manage the available fibre channel paths, you need to use a multipathing solution (e.g., Sun’s MPXIO, EMC’s powerpath, or Veritas’ DMP, etc.) on the server. VMWare ESX server comes with it’s own multipathing solution (it is better defined as path failover), and provides the esxcfg-mpath utility to view the path information for all of the targets available on a server:
$ esxcfg-mpath -l
Disk vmhba0:0:0 /dev/sda (70007MB) has 1 paths and policy of Fixed
Local 2:4.0 vmhba0:0:0 On active preferred
Disk vmhba0:1:0 /dev/sdb (70007MB) has 1 paths and policy of Fixed
Local 2:4.0 vmhba0:1:0 On active preferred
Disk vmhba1:0:0 /dev/sdc (51200MB) has 4 paths and policy of Most Recently Used
FC 4:4.0 10000000c9413167<->50060161082006e2 vmhba1:0:0 On active preferred
FC 4:4.0 10000000c9413167<->50060169082006e2 vmhba1:1:0 Standby
FC 4:5.0 10000000c9413168<->50060160082006e2 vmhba2:0:0 On
FC 4:5.0 10000000c9413168<->50060168082006e2 vmhba2:1:0 Standby
Disk vmhba1:0:1 /dev/sdd (51200MB) has 4 paths and policy of Most Recently Used
FC 4:4.0 10000000c9413167<->50060161082006e2 vmhba1:0:1 On active preferred
FC 4:4.0 10000000c9413167<->50060169082006e2 vmhba1:1:1 Standby
FC 4:5.0 10000000c9413168<->50060160082006e2 vmhba2:0:1 On
FC 4:5.0 10000000c9413168<->50060168082006e2 vmhba2:1:1 Standby
You can also retrieve this information from the virtual infrastructure client, but knowing the CLI can be invaluable should a catastrophic failure occur. The more I work with ESX server 3.0, the more I dig it!