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October 04, 2010


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Dan Muntz

The only way a pNFS files data store can span vendors would be through something like FedFS, and then it's simply the namespace doing the spanning. Data servers in a pNFS files setup use a vendor-specific "control protocol" to interact with metadata servers. There is no standard covering these control protocols, and they are tightly-coupled to the vendor's server implementation.

iwan 'e1' Rahabok

Hi Chad, thanks for another excellent post.

When you said that "due to the NFSv3 client in vSphere, each _datastore_ will have all the traffic going to a single MAC address (which one will be determined by your exact _config_)", do you mean that we can configure which pNIC to use for which datastore? How do I configure that (I guess it has to be CLI on each ESX).

If we use Load Based Teaming in vSphere 4.1, will that help when we have a pair of 1 GE pNIC dedicated for NFS?

Many thanks from Singapore
e1 at vmware dot com

Chad Sakac

@e1 - that's a common misunderstanding. NIC teaming/loadbalancing (802.3ad) works by picking a link when a TCP session is first established. Which one is picked based on a hash of some sort (source/dest IP, source/dest MAC).

If it's static link aggregation, that selected link is used constantly for that TCP session.

If it's dynamic link aggregation, the link that was selected can be changed based on load.

BUT only a single link is used at any given time.

That's one of the key things - NFS v3 uses a single session per mount, and therefore a single link.

So - no matter how you configure, if you're using 1GbE (as opposed to 10GbE), expect to see about 80MBps as the max for the datastore if 100% read or write, and about 160 MBps as the max for the datastore if you have a 50/50 read/write workload (since 1GbE is actually bi-directional).

That's why if you want to increase throughput you need to have multiple datastores, and it's also ONE of the reasons why changes in the NFS client behavior in vSphere would be a big deal.

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