I wrote a few weeks ago about Infinio and their NFS acceleration product for NFS datastores on vSphere. Since then I realised that one of the clients I’m working at is an ideal candidate for the product. The customer has an aged VDI environment containing some old ESXi hosts and backed by an old low spec NetApp array. The performance of the VDI desktops is limited by the amount of RAM in the ESXi servers and the speed of the storage.
Due to the lack of RAM any VM that is not logged onto is suspended, then when the use logs back on it is resumed, resulting in a lot of disk read activity. The disks in the NetApp are running at over 50% service time so latency is high from the array, making every disk access slow. It is much cheaper for the client to buy more RAM for their ESXi servers than more trays of disk for the NetApp. If the ESXi servers were upgraded from 128GB of RAM to 256 GB and each had an Infinio appliance deployed then the performance problems should dry up pretty fast. The extra RAM would relieve stress on the ESXi hosts and allow more of the desktop VMs to run with 2GB of RAM and the Infinio caches would allow the NetApps to spend their time servicing write IO. The RAM upgrade would be needed otherwise the Infinio appliance would exacerbate the shortage of RAM in the ESXi hosts and any storage improvements would be invisible under the degradation due to RAM stress.
It is important to recognise that in VDI there is a relationship between VM configured RAM and disk activity, a VM with ample RAM will do little disk reading once it’s booted but a VM short of RAM will thrash it’s disk all day. More RAM is a good solution to disk performance and an Infinio or Pernix cache can further reduce the load on the array and improve VM disk performance.