User guide

addition to the environmental benefits of heating and cooling, you can save 3U of rack space per shelf. For

a real-world deployment, a NetApp solution (with Flash Cache as a primary component) would typically

replace several such storage shelves; therefore, the savings could be considerably higher.

3.4.7 NetApp Flash Cache and PAM

NetApp Flash Cache and PAM are hardware devices that extend the native Data ONTAP TSCS capabilities.

Flash Cache increases the amount of available cache which helps reduce virtual desktop storm activities. More

details of Flash Cache will be discussed later in this document. For more details on NetApp Flash Cache

technology, visit http://www.netapp.com/us/products/storage-systems/flash-cache/flash-cache-tech-specs.html

Note: For the remainder of this document, the use of Flash Cache will represent both the Flash Cache and PAM modules.

3.4.8 NetApp Write Optimization

Virtual desktop I/O patterns are often very random in nature. Random writes are the most expensive operation for

almost all RAID types because each write operation requires more than one disk operation. The ratio of VDI client

operation to disk operation also depends on the RAID type for the back-end storage array. In a RAID 5

configuration on a traditional storage array, each client write operation requires up to four disk operations. Large

write cache might help, but traditional storage arrays still require at least two disk operations. (Some coalescing of

requests will happen if you have a big enough write cache. Also, there is a chance that one of the reads might

come from read cache.) In a RAID 10 configuration, each client write operation requires two disk operations. The

cost of RAID 10 is very high compared to RAID 5. However, RAID 5 offers lower resiliency (protection against

single disk failure). Imagine dual disk failure in the middle of the day, making hundreds to thousands of users

unproductive.

With NetApp, write operations have been optimized for RAID-DP by the core operating system Data ONTAP and

WAFL® since their invention. NetApp arrays coalesce multiple client write operations and send them to disk as a

single IOP. Therefore, the ratio of client operations to disk operations is always less than 1, as compared to

traditional storage arrays with RAID 5 or RAID 10 which require at least 2x disk operations per client operation.

Also, RAID-DP provides the desired resiliency (protection against dual disk failure) and performance, comparable

to RAID 10 but at the cost of RAID 5

3.4.9 Flexible Volumes and Aggregates

Flexible volumes (also known as FlexVol volumes) and aggregates provide pools of storage. This storage

virtualization allows the performance and capacity to be shared by all desktops in the volume or aggregate. Much

like the way that Citrix virtualizes computing resources, NetApp virtualizes the storage resources.

3.4.10 Operational Agility

Implementation and management complexities associated with deploying a Citrix XenDesktop solution are

another potential barrier to VDI adoption. The Citrix StorageLink provides integration between XenServer and

NetApp for rapidly provisioning, managing, configuring, backing up and disaster recovery capability of a Citrix

XenDesktop implementation. Citrix StorageLink is available with XenServer Enterprise Edition, and requires the

installation of the StorageLink Gateway service on a Windows Server virtual machine or physical server.