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Anyone familiar with NetApp Single_image mode?

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We just upgraded the old heads in our cluster. The new models support cfmode single_image, which NetApp strongly recommended we switch to.

We have each host in our ESX cluster dual homed to the SAN Fabric.

Since we switched our Filer cluster to single_image, each of the hosts now have 4 paths to each LUN instead of 2 paths.

Is this normal? The thing is, when we upgraded our NetApp cluster at our co-lo site, we still only see 2 paths to each LUN.

I thought single_image was supposed to present only 1 WWN to the fabric...

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ankaiser
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This is normal. In single image mode each head presents all of its adapters as valid path to the LUN, even when the LUN is not owned by the head. If a path to the wrong head is actually used outside of failover mode, the traffic is routed via the Infiniband cluster interconnect and results in a warning issued by ONTAP. So it may be necessary to manually change the preferred path on the ESX.

Having a single target WWN does not imply a single path, instead all possible paths are shown separately. Operating systems and drivers have different strategies to handle them though. Some support load balancing over all or part of the paths, some detect path priorities automatically, on others you have to control path usage manually.

If you cannot see all possible paths, check the SAN configuration.

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ankaiser
Enthusiast
Enthusiast

This is normal. In single image mode each head presents all of its adapters as valid path to the LUN, even when the LUN is not owned by the head. If a path to the wrong head is actually used outside of failover mode, the traffic is routed via the Infiniband cluster interconnect and results in a warning issued by ONTAP. So it may be necessary to manually change the preferred path on the ESX.

Having a single target WWN does not imply a single path, instead all possible paths are shown separately. Operating systems and drivers have different strategies to handle them though. Some support load balancing over all or part of the paths, some detect path priorities automatically, on others you have to control path usage manually.

If you cannot see all possible paths, check the SAN configuration.

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