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Monthly Archives: November 2015

Scaling Performance for VAIO in vSphere 6.0 U1

by Chien-Chia Chen

vSphere APIs for I/O Filtering (VAIO) is a framework that enables third-party software developers to implement data services, such as caching and replication, to vSphere. Figure 1 below shows the general architecture of VAIO. Once I/O filter libraries are installed to a virtual disk (VMDK), every I/O request generated from the guest operating system to the VMDK will first be intercepted by the VAIO framework at the file device layer. The VAIO framework then hands over the I/O request to the user space I/O filter libraries, where a series of third party data service operations can be performed against the I/O. After processing the I/O, user space I/O filter libraries return the I/O back to the VAIO framework, which continues the rest of the issuing path. Similarly, upon completion, the I/O will first be processed by the user space I/O filter libraries before continuing its original completion path.

There have been questions around the overhead of the VAIO framework due to its extra user-to-kernel communication. In this blog post, we evaluate the performance of vSphere APIs for I/O Filtering using a null I/O filter and demonstrate how VAIO scales with respect to the number of virtual machines and outstanding I/Os (OIOs). The null I/O filter accepts each I/O request and immediately returns it.

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Dynamic Host-Wide Performance Tuning in VMware vSphere 6.0

by Chien-Chia Chen

Introduction

The networking stack of vSphere is, by default, tuned to balance the tradeoffs between CPU cost and latency to provide good performance across a wide variety of applications. However, there are some cases where using a tunable provides better performance. An example is Web-farm workloads, or any circumstance where a high consolidation ratio (lots of VMs on a single ESXi host) is preferred over extremely low end-to-end latency. VMware vSphere 6.0 introduces the Dynamic Host-Wide Performance Tuning  feature (also known as dense mode), which provides a single configuration option to dynamically optimize individual ESXi hosts for high consolidation scenarios under certain use cases. Later in this blog, we define those use cases. Right now, we take a look at how dense mode works from an internal viewpoint.

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