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Caching and SAN accelerators
Using a caching device or a SAN accelerator can make up for slower performing storage devices and provide more IOPS to deal with boot storms and other periodic I/O peaks. It can also save money because you may be able to use less-expensive storage devices but still be able to handle your VDI I/O workloads. Caching device like NetApp's Flash Cache can make a huge difference and can greatly increase the number of IOPS your storage is capable of. Configure your caching for the appropriate areas; events like boot storms generally are very read intensive so a larger read cache will make a big difference.
|Virtual machine RAM and paging|
The amount of RAM assigned to a virtual machine can have a big impact on its performance. If you don't assign enough RAM, the operating system will start paging to disk, which can greatly increase the amount of disk I/O -- a situation you want to avoid as the needless storage I/O can degrade performance. Assigning too much RAM can cause swapping at the virtualization layer if a host has overcommitted memory, which can also degrade storage performance. It's OK to overcommit host memory and it's commonly done with virtual desktop infrastructure (VDI); just make sure you don't completely exhaust your host memory.
SAN accelerators are a great way to add a high-performance caching layer in front of your existing storage device. FalconStor's Network Storage Server (NSS) SAN Accelerator for VMware View is an easy-to-deploy appliance that can improve a storage system's performance. It may even let you use low-cost SATA drives for your VDI storage and still get adequate performance.
This was first published in March 2011