SAN experts help: multipathing

[kfkehua]

Dear all Vmware and SAN experts, got a question regarding multiple paths, is it configured at the ESX side or on the SAN side.

From what I can tell there are no places in the vi client to configure multiple paths. So I assume ESX automatically picks up the multiple paths if they are confirgured properly on the SAN side side?

Thanks very much.

[LE2Strat]

2 ways to get to path management within VI client.\

#1. Highlight your ESX server and go to the configuraiton tab. Go to the storage adapter section, high one of your HBA's, right click one of your targets and click manage paths.

#2. You can also get to the same menu above by going to the storage section, right click one of your stroage locations, go to properties, then click the mange paths button in the lower right hand corner.

From there you can see waht is the active path, and your SAN identifiers.

Here is a summary of the the difference between each path policy you can set:

Fixed - When a data store is set to use the fixed policy, traffic travels down only the preferred path, unless it is unavailable, at which time it will fail over to a secondary active path. When the preferred path returns, traffic will resume traveling on that path. This is the default multipathing policy for storage arrays with active/active storage processors.

Most Recently Used (MRU) - Similar to a fixed policy, when designated as MRU, ESX will use a path until that path is no longer available. When the first path returns, the MRU policy will not switch back; it will continue to use the same path until it is no longer available. MRU is the default policy for storage arrays with active/passive storage processors.

Round Robin -- The Round Robin multipathing policy is officially listed as experimental; it will load-balance the I/O requests across all available paths

ESX will automatically pick up all of the paths as long as they are zoned correctly on your Fibre Channel switches so you should see all of your available paths int he manage path screen.

[Jae_Ellers]

there are also some utilities from certain manufacturers, such as NetApp, that need to be used or at least make configuration easier. In a NetApp cluster there's a path thru the primary controller for a lun and also the secondary controller. Should the ESX server see the path on the secondary first and use that the NetApp will recognize this isn't the most optimal path and start to log configuration errors. Running config_mpath from the host will configure the paths in an optimal fashion. This can also be done manually to avoid errors, but gets cumbersome once there are more than a couple hosts and luns.

[kfkehua]

My question is for example, if the server has two HBA's going to the same storage. Should the paths then automatically be listed under the "manage paths" ?

Or something needs to be done manually in order for ESX to realize that these two paths go to the same storage?

[BUGCHK]

If the storage environment has been configured correctly, ESX server automatically recognizes all paths and binds them to the 'canonical path' - you need not and cannot change that. What you can do is, disable paths or declare a path as a preferred one.