How NTFS Causes IO Bottlenecks on Virtual Machines

Bob NolanFrom a contributed article on VMblog.com by Bob Nolan, Raxco President and CEO.

Virtualized platforms can suffer from resource contention issues. Why wouldn’t performance be an issue when there are multiple instances of Windows Server running on the same physical machine?  Performance issues on virtual machines stem from their competition for a finite pool of CPU, memory and disk resources. Of these, disk resources are the most important since the disk is the slowest component of the three. To the extent you are hammering away at the disk, you are also consuming excess CPU and memory, depriving other VMs access to these resources. In this two-part article, we will look at one potential source of IO problems, its impact on virtual performance and possible solutions.

  • Just like their physical counterparts, performance issues on virtual machines stem from their competition for a finite pool of CPU, memory and disk resources.
  • SIOC is a practical workaround, but it doesn’t solve the problem. Rather, it trades symptoms.
  • The source of resource contention in many virtualized environments is caused by the Windows NT File System (NTFS).
  • When IO performance issues arise, the tendency is to look at the storage as the problem. But if the IO load from the guest is creating a latency issue by saturating the queues, isn’t it likely NTFS is the source?
  • To fully understand the relationship between NTFS and poor virtualization performance, we need to understand what is going on inside the Windows guest.

The remainder of this discussion details the NTFS behavior that leads to IO bottlenecks and how this relates to disk latency and throughput issues.





Category: PerfectDiskStorageVirtualization

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