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Virtualization and Disk Performance
To Virtualize Something Means To Make Something That Doesn?t Actually Exist Appear To Exist
This equates to hierarchical fragmentation or more simply fragmentation-within-fragmentation. The black lines in Image6 (below) represent disk I/O mappings of the virtual disk file fragments to the host system in a Hosted Architecture.
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Machine Virtualization Architectures and I/O:
Given either of two predominant virtualization architectures (Hosted orHypervisor) remember that the virtual machines are emulating hardware andmay not emulate the exact specifications. For example, a high-end video card may not be emulated ina host system with all the advanced capabilities.
The Hypervisor architecture (above) removes the requirement for a host operating system and improves overall virtual systems performance.
As demonstrated earlier, Disk I/Os generated from virtual systems (Hosted Architecture) can suffer from increased software stack processing. This means that disk I/O has to go up and down software layers that abstract the physical hardware. In a Hosted Architecture, a low level disk request in a guest system is translated into a user level call in the host system. With the likely loss of disk caching at the guest level (hardware support consideration), and limited queuing ability, this process will not be as speedy as a direct physical hardware call by the host system.
In summary, server virtualization establishes a symbiotic relationship, so it is important to remember that generating disk I/O in one virtual machine slows I/O to the disk from other virtual systems, no matter the architecture. Fragmentation is both increasingly substantial in virtual machines environments (hierarchical in Hosted Architecture) and compounds the disk bottleneck more so than on conventional systems (shared resource).
For the future, with the opening of proprietary formats for third party development, virtualization-ready hardware from Intel and AMD (improved hardware support and access), operating system advancements (Hypervisor will be an integral part of Windows Longhorn) and technology partnerships such as that between Diskeeper and Microsoft, look for continuing improvements to disk performance as virtualization gets further entrenched in everyday IT.
Improving Disk Performance for Virtual Servers:
1. Run advanced automatic defragmentation on Host and all Guest operating systems. Make sure the software is disk-resource friendly, as intrusive defragmentation with manual or basic tools can cause more problems than they solve.
2. Use basic built-in or more advanced third-party tools (such as Diskeepers FragShield) to properly adjust MFT and paging file settings on the host and/or guest operating systems.
3. Incorporate the following industry expert recommended disk subsystem and partitioning strategies:
- To minimize fragmentation of the virtual disks, pre-allocate their size if possible just be sure to monitor and quota disk space.
- Separate the host operating system onto a separate physical disk (spindle).
- Keep the host paging file on a physical disk (spindle) separate from those of the virtual disks.
- Create separate logical partitions on the host system for each virtual system. This is especially true for dynamically expanding virtual hard disks.
- Use high performance SCSI hard disks, and ideally a SAN or RAID back end.
- Compact the virtual hard disks. Make sure to address fragmentation as part of compaction process, both before and after compaction.
Best Practices References:
VM Performance Tips (Michael Otey - Windows IT Pro): http://www.windowsitpro.com/Article/ArticleID/48726/48726.html
How to Improve Disk I/O Performances with VMware Workstation 5-(Alessandro Perilli): http://www.virtualization.info/2005/11/how-to-improve-disk-io-performances.html
Virtual Server Improving Performance Microsoft Corporation: http://www.microsoft.com/technet/prodtechnol/virtualserver/2005/proddocs/vs_operate_using_perfTune_tune.mspx?mfr=true
Configuring Hard Disk Storage in a Virtual Machine VMware Inc.: http://www.vmware.com/support/ws45/doc/disks_config_ws.html
Diskeeper and Microsoft Collaborate to Offer Advanced Virtual Server Performance Microsoft Corporation: http://www.microsoft.com/presspass/features/2006/apr06/0403virtualizationqa.mspx
Virtual Server 2005 Best Practices Microsoft Corporation: http://www.microsoft.com/technet/prodtechnol/virtualserver/2005/proddocs/vs_deploy_reqs.mspx?mfr=true
Diskeeper Corporation.
7590 N. Glenoaks Blvd.
Burbank, CA 91504
800-829-6468
www.diskeeper.com
© Diskeeper Corporation 2006 All Rights Reserved. Diskeeper, The Number One Automatic Defragmenter, and Frag Shield are either registered trademarks or trademarks of Diskeeper Corporation. Microsoft, Windows and Virtual Server are either registered trademarks or trademarks of Microsoft Corporation in the United States and/or other countries. VMware is a trademark of VMware, Inc. Virtuozzo is a trademark of SWsoft, Inc. All other trademarks are the property of their respective owners.
Related Sites: Storage , IBN - Storage , IBN - Hardware , IBN - IT Business Net
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