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Monthly Archives: October 2015

VMware Virtual SAN Stretched Cluster Best Practices White Paper

VMware Virtual SAN 6.1 introduced the concept of a stretched cluster which allows the Virtual SAN customer to configure two geographically located sites, while synchronously replicating data between the two sites. A technical white paper about the Virtual SAN stretched cluster performance has now been published. This paper provides guidelines on how to get the best performance for applications deployed on a Virtual SAN stretched cluster environment.

The chart below, borrowed from the white paper, compares the performance of the Virtual SAN 6.1 stretched cluster deployment against the regular Virtual SAN cluster without any fault domains. A nine- node Virtual SAN stretched cluster is considered with two different configurations of inter-site latency: 1ms and 5ms. The DVD Store benchmark is executed on four virtual machines on each host of the nine-node Virtual SAN stretched cluster. The DVD Store performance metrics of cumulated orders per minute in the cluster, read/write IOPs, and average latency are compared with a similar workload on the regular Virtual SAN cluster. The orders per minute (OPM) is lower by 3% and 6% for the 1ms and 5ms inter-site latency stretched cluster compared to the regular Virtual SAN cluster.

Figure 1a.  DVD Store orders per minute in the cluster and guest IOPS comparison

Guest read/write IOPS and latency were also monitored. The read/write mix ratio for the DVD Store workload is roughly at 1/3 read and 2/3 write. Write latency shows an obvious increase trend when the inter-site latency is higher, while the read latency is only marginally impacted. As a result, the average latency increases from 2.4ms to 2.7ms, and 5.1ms for 1ms and 5ms inter-site latency configuration.

Figure 1b.  DVD Store latency comparison

These results demonstrate that the inter-site latency in a Virtual SAN stretched cluster deployment has a marginal performance impact on a commercial workload like DVD Store. More results are available in the white paper.

Measuring Cloud Scalability Using the Weathervane Benchmark

Cloud-based deployments continue to be a hot topic in many of today’s corporations.  Often the discussion revolves around workload portability, ease of migration, and service pricing differences.  In an effort to bring performance into the discussion we decided to leverage VMware’s new benchmark, Weathervane.  As a follow-on to Harold Rosenberg’s introductory Weathervane post we decided to showcase some of the flexibility and scalability of our new large-scale benchmark.  Previously, Harold presented some initial scalability data running on three local vSphere 6 hosts.  For this article, we decided to extend this further by demonstrating Weathervane’s ability to run within a non-VMware cloud environment and scaling up the number of app servers.

Weathervane is a new web-application benchmark architected to simulate modern-day web applications.  It consists of a benchmark application and a workload driver.  Combined, they simulate the behavior of everyday users attending a real-time auction.  For more details on Weathervane I encourage you to review the introductory post.

Environment Configuration:
Cloud Environment: Amazon AWS, US West.
Instance Types: M3.XLarge, M3.Large, C3.Large.
Instance Notes: Database instances utilized an additional 300GB io1 tier data disk.
Instance Operating System: Centos 6.5 x64.
Application: Weathervane Internal Build 084.

Testing Methodology:
All instances were run within the same cloud environment to reduce network-induced latencies.  We started with a base configuration consisting of eight instances.  We then  scaled out the number of workload drivers and application servers in an effort to identify how a cloud environment scaled as application workload needs increased.  We used Weathervane’s FindMax functionality which runs a series of tests to determine the maximum number of users the configuration can sustain while still meeting QoS requirements.  It should be noted that the early experimentation allowed us to identify the maximum needs for the other services beyond the workload drivers and application servers to reduce the likelihood of bottlenecks in these services.  Below is a block diagram of the configurations used for the scaled-out Weathervane deployment.


For our analysis of Weathervane cloud scaling we ran multiple iterations for each scale load level and selected the average.  We automated the process to ensure consistency.  Our results show both the number of users sustained as well as the http requests per second as reported by the benchmark harness.


As you can see in the above graph, for our cloud environment running Weathervane, scaling the number of applications servers yielded nearly linear scaling up to five application servers. The delta in scaling between the number of users and the http requests per second sustained was less than 1%.  Due to time constraints we were unable to test beyond five application servers but we expect that the scaling would have continued upwards well beyond the load levels presented.

Although just a small sample of what Weathervane and cloud environments can scale to, this brief article highlights both the benchmark and cloud environment scaling.  Though Weathervane hasn’t been released publicly yet, it’s easy to see how this type of controlled, scalable benchmark will assist in performance evaluations of a diverse set of environments.  Look for more Weathervane based cloud performance analysis in the future.