White Papers

BP1018 Sizing and Best Practices for Citrix XenDesktop with Dell EqualLogic Storage 32
6 Sizing guidelines for EqualLogic SANs
Virtual desktop usage in enterprise environments follows predictable I/O patterns. For example, at the
beginning of the workday most employees login into their desktops within a relatively short timeframe.
After the login storm, periods of high and low steady state application activities will occur. For
example, high user activity on their workstations during morning and afternoon hours and low activity
during break hours would be expected. These phases of activity cause different I/O patterns and loads
in the VDI environment SAN. There may also be some rare scenarios such as recovery after an
unexpected power shutdown which can cause a boot storm. The storage array should be able to
handle this type of workload within acceptable latency limits.
The first step to design and deploy a storage infrastructure for VDI is to understand the storage
characteristics and performance requirements of the application. The most important storage
characteristics to be considered while designing the storage infrastructure are:
Capacity
Performance
o IOPS
o Average disk latency
Type of I/O (Sequential or Random)
o Read and write ratio
In this chapter, we will summarize the key performance and capacity guidelines specifically focused
on Citrix XenDesktop VDI environments deployed using EqualLogic storage. These guidelines are
based on the results and key observations captured while completing the tests explained in section 5.
6.1 Storage capacity considerations
6.1.1 vDisk capacity requirements
The vDisk size was determined based on these key considerations:
- The size of the Windows 7 OS image.
- Generally it is recommended to keep at least one or two clean backups of the base OS images.
- Also there may be some requirements such as keeping multiple versions of vDisks in case of
major software updates or new patches.
The size of the OS image depends on the specific use case and also the number of applications and
software installed. These estimates were based on an OS installation with only the applications to run
the Login VSI workload. These estimates may not accurately reflect the required sizes of vDisks in
every configuration, but they provide a guideline to determine space requirements for vDisk images
for task worker I/O profiles.
We recommend using standard mode vDisks where the single master OS image is streamed to all
virtual desktops over the network. This type of implementation is very efficient because administrators
need to manage and maintain a single image instead of each individual virtual desktop and it reduces
storage requirements significantly because only one OS image needs to be stored.