Virtualization has the potential to reduce costs by saving money on physical footprint,
power, hardware costs, and support personnel.
The savings can only be realized if the virtual guests are properly maintained.
In a virtual environment, there are multiple instances of Windows Server competing
for finite resources on a single host system. This can lead to resource contention
and performance issues. A key to the successful management of a virtualized environment
is making sure there are adequate resources available from the host system to support
all of the virtual guest systems.
As the number of virtual machines increase, the disk I/O load on the host drive
increases proportionally. System administrators must continually monitor and balance
the disk I/O loads for the virtual machines against the capacity of the host to
ensure that optimal disk performance can be maintained. The disk drive is the slowest
resource in any computing system, so anything that can be done to speed up disk
availability is a plus for the virtual user.
File and Free Space Fragmentation and Virtual System Performance
Fragmentation occurs when the file system can't create a file in a contiguous string
of logical clusters. File creation, deletion and extension all exacerbate file fragmentation
as the disk fills up and the remaining free space is scattered around the disk.
With continued use, files and free space fragmentation degrade overall system performance.
In a virtual environment, the effects of fragmentation can be even more pronounced.
Each virtual machine is running an instance of the Windows file system and incurring
its own fragmentation. As fragmentation increases, the demand for additional CPU
and I/O resources increases proportionally.
This increasing demand can have a negative impact on the performance of other virtual
machines on the same host, since they are competing for the same resources. Several
competing virtual machines will have an adverse effect on the host platform performance,
which may not be able to provide adequate CPU and I/O resources to its guests.
The excess I/O per second (IOPS) generated by fragmentation adversely affect several
quantifiable areas:
- Each fragment creates a scsi command to be processed by the storage stack, increasing
hypervisor overhead
- Fragmentation inhibits the ability to perform larger and more efficient I/O, with
an adverse effect on throughput
- As the number of scsi commands increase, disk latency degrades due to
excess physical accesses to the disk
- In combination, all of the above impact performance and productivity.
Disk Defragmentation Improves Virtualization Performance
Defragmentation of Windows guest systems provides the following benefits:
- Reduces the total I/O count crossing the storage stack, lowering hypervisor overhead
- Fewer and larger I/O improves throughput
- Fewer and larger I/O improves disk latency
- Overall system I/O performance is better and there is less contention for resources.
Defragmentation can take place on the virtual disk (Windows guest OS) or on the
physical disk (Windows host OS). Defragmentation on the virtual disk optimizes
the disk I/O and minimizes the resource demand for that virtual machine. Defragmentation
on the physical disk (Windows host OS) optimizes the core disk resources available
to all the guests and compounds the benefit of defragmenting solely on the guest
virtual disks.
There is still a benefit to be realized from defragmenting virtual disks with Windows
guests when the host is running a non-Windows OS, as with VMware's ESX Server.
The Windows guests still compete for the host resources, so keeping the guest in
optimal I/O condition minimizes the demand on the host regardless of the OS. A secondary
benefit of keeping the Windows guests defragmented and lowering the resource demand
is that it may allow you to support additional guests on the same host, thereby
reducing the need for continuous load balancing.
Automatic Disk Defragmentation - Not Always a Good Idea
Automatic disk defragmentation is a feature available with third party enterprise-capable
disk defragmentation products. The premise behind automatic disk defragmentation
is that instead of scheduling disk defragmentation to run on a fixed interval, the
automatic defragmentation mode detects when the system is idle and initiates a defrag
pass only when the system is idle. While this saves the system administrator the
time needed to set fixed interval schedules for the virtual systems, it does come
with a serious downside.
Part of the balancing act that comes with virtualization is making sure the host
can provide adequate resources for the virtual systems to do their work. In the
case of automatic defragmentation of virtual systems, it is possible to consume
host resources to the detriment of working virtual machines. For example, a physical
system is set up with five (5) virtual Windows guests. Automatic disk defragmentation
is invoked to run on the virtual systems whenever they are idle. At some point,
two of the virtual systems become idle and the remaining three are busy. As defined,
the automatic disk defragmentation would start on the two idle virtual systems without
regard to the demand for resources from the three busy virtual systems. This lack
of virtual awareness can cause a resource bottleneck on the working virtual systems,
since the host system cannot satisfy the resource demand of all the Windows guests
simultaneously. In this case, the system administrator would have to make some decisions
about moving the virtual machines to another server or stopping the defragmentation
which keeps the disks in optimal running order. Virtualization Awareness addresses
this issue.
Virtualization Awareness - A New Way to Maintain System Performance
System administrators should not have to decide between getting the work done and
good system performance. As we showed in the case above, the downside of automatic
disk defragmentation is that it can strangle the host resources to the performance
detriment of the all the virtual systems.
PerfectDisk® with Virtual Awareness is the answer to this dilemma. Virtualization
Awareness monitors the availability of the physical host resources and precludes
automatic disk defragmentation from running if adequate resources are not available.
In the example above, virtualization awareness would prevent the automatic defragmentation
of the two idle systems if the host did not have sufficient resources to support
the working virtual machines and the defragmentation.
The benefit of Virtualization Awareness to the organization and the system administrator
is that virtual disks can be optimized for top performance, which eases the total
resource burden on both the virtual and the host systems. Further, this can be accomplished
in a fully automated manner without administrator intervention and without concern
about the impact on host resources.
The same applies to any Virtual Desktop Infrastructure (VDI) implementations. Virtualization
Awareness will keep multiple instances of virtual desktops set for automatic defragmentation
from consuming all the available resources on the host. Virtualization Awareness
will permit automatic defragmentation up to a dynamic threshold level based on the
available host resources.
The PerfectDisk product line of disk defragmentation and optimization tools provides
all-encompassing solutions to optimize performance in your entire virtual infrastructure:
PerfectDisk vSphere
Maximize the efficiency of the physical host’s resource utilization
by optimizing guests to eliminate I/O throughput and I/O latency bottlenecks. Virtual
infrastructure awareness technology monitors resource availability at the physical
host level and allows optimizations to occur dynamically between virtual guests
so as to completely eliminate the resource contention caused by simultaneous optimizations.
PerfectDisk Hyper-V
Total automation and flexibility combined with robust central management
to provide complete defragmentation of your production Hyper-V environment. PerfectDisk
Hyper-V utilizes patent-pending Virtual Aware defragmentation to improve Windows
Server 2008 Hyper-V performance while eliminating resource contention, so your virtual
environment runs better than ever.
PerfectDisk VMware Workstation
Improve the performance in your VMware Workstation for Windows
environment in accordance with VMware recommendations. Boost performance on both
the physical host and virtual guests, while reducing resource consumption on both.