users with virtual desktops addresses some issues
there are some “gotchas” that you need to consider
By Budi Darmawan
Virtual Desktop Infrastructure is an attempt to
provide enterprise wide employees a unified, managed environment for their
workspace. The virtual desktop allows each employee to have his or her desktop
system within the datacenter (i.e.: in the cloud), while they connect to it
using a secure connection from their pervasive devices such as smart phone, tablet,
laptop or home computer.
Desktop and Cloud
The virtual desktop infrastructure is quite similar
to a cloud system. Both rely on virtualization of hardware and software and
both will benefit from the sharing of resources in the datacenter and
integrated management from the datacenter. However, due to their workload
profile, there are significant differences.
The following lists the difference in the workload
profile for virtual desktop against a more ‘traditional’ cloud or virtualization:
Number of users: Virtual desktop is used
by ALL employees; it is being used for the employee’s interactive day-to-day
workload. Traditional virtualized cloud is mainly used as a special-purpose
system, such as application servers, or test environments.
Load type: Virtual desktop load is
mainly interactive, made up of things like mouse clicks and screen refreshes,
with occasional disk access, per user. These activities increase network load.
Virtualized cloud for servers is mainly offline background work which puts the
burden on CPU and memory.
Active time: Virtual desktop is mainly
active on prime shift when employees are working, so for a follow the sun
operation, load sharing can be performed for different shifts and locations.
Base system: Virtual desktops are
usually more uniform than traditional test or server environments; corporate IT
departments have standards on what employee can run.
Virtual Desktop implementation on a standard cloud
system would generate some issues due to the above load profiles.
· One of the main problems on early
implementation of virtual desktop is disk access for multiple users. This
access does not scale linearly. One of the measurements of this is called IOPS
(Input-Output Operations per Second); as different users access different part
of the physical disk, and each of the desktop environment can be hosted on
different area of the same disk, they will eventually compete for disk access. The
latency for this would increase exponentially as more contention arises between
· Branch office users would generate
network traffic for mouse movement and screen refreshes that competes with
actual production (money-making) transactions. This eventually can present a
bottleneck in the Wide Area Network (WAN) infrastructure of the enterprise.
· Idle capacity as the users leave their
virtual desktop open (not switched off) but not being used. This creates a
processing overhead that may impact system-wide performance.
Depending on the issues, several alternative methods
have been developed to address them.
· Due to the uniform nature of the image,
the number images for virtual desktops can be easily shrunk down to a small set
of corporate images.
· Smart buffering of images in memory can
significantly reduce the IO contention for high number of users. The buffering,
coupled with the fact that there is a limited set of corporate images, allows
(with enough resources) images to be completely stored in memory, reducing all
read operations and batch performing the write operations.
· Creating branch-level servers which also
cache the virtual desktop images, provides user interface operations locally.
This will significantly remove the WAN network pressure.
· Detecting idle sessions and shutting
them down in an automated fashion will help on alleviate overhead from systems
that are not properly released after the employee disconnects.
Some significant requirements for the Virtual
Desktop Infrastructure include:
Platform support (for the desktops)
IBM Virtual Desktop supplies the solution for the
above requirements. It has uniquely designed storage optimization that allows
most of the virtual desktop to run from a copy in memory. This reduces the
desktop user IO requirements significantly. With the avoidance of IO needs, IBM
Virtual Desktop provides significant scalability compared to having an individual,
dedicated disk for each desktop user.
IBM Virtual Desktop supports both Windows and Linux
based desktops and therefore allows portability between the different desktop
For more information on IBM Virtual Desktop, refer
a Senior Technical Enablement Specialist with IBM Software Services for Tivoli.
His areas of expertise include TSAM, ISDM and Smart Cloud Orchestrator. He has
been with IBM since 1990 and has written more than 40 IBM Redbooks.
He lives in Austin, Texas.