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VMware, ReadyNAS, NFS, and extremely high latency

I have spent plenty of time researching and dealing with this problem of extremely high latency between my ESXi VMware hosts and the NFS datastores on my ReadyNAS 2100.  It’s ridiculous how stupidly simple the solution was, and how not one of the posts I’ve found in a Google search have pointed this simple setting out.

Of course, the first thing you should do is ensure that you following this ReadyNAS article on how to optimize the ReadyNAS performance.

However, for an existing ReadyNAS NFS  datastore that is experiencing extremely high latency, there may be a specific setting associated with the NFS share that is causing your high latency.   To verify, login to your ReadyNAS web interface, then go to “Shares -> Share Listing” and click on the NFS edit icon for the share that your ESXi host is mapped to.

Scroll down to the Advanced NFS Options and ensure that the “Enable sync mode” is UNCHECKED.

ReadyNAS 2100 high latency disable sync mode

Of course you need to be aware of the potential issues with data integrity when unexpected shutdowns occur.  But if you’ll notice the graphs below, you can see that my latency went from the 50ms-300ms range down to less than 10ms.   This setting it seems is nearly impossible to live with in my configuration.

Latency during vMotion migrate of storage
ReadyNAS NFS vMotion migrate with and without sync mode enabled

ReadyNAS NFS Latency before & after disabling sync mode
ReadyNAS NFS Latency with and without sync mode enabled


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