VROOM!

VMware Fault Tolerance (FT), based on vLockstep technology and available with VMware vSphere, easily and efficiently provides zero downtime and zero data loss for your critical workloads. FT provides continuous availability in the event of server failures by creating a live shadow instance of the primary virtual machine on a secondary system.  The shadow VM (or secondary VM), running on the secondary system, executes sequences of x86 instructions identical to the primary VM, with which it proceeds in vLockstep.  By doing so, if catastrophic failure of the primary system occurs it causes an instantaneous failover to the secondary VM that would be virtually indistinguishable to the end user. While FT technology is certainly compelling, some potential users express concern about possible performance overhead. In this article, we explore the performance implications of running FT in realistic scenarios by measuring an FT-enabled environment based on the heterogeneous workloads found in VMmark, the tile-based mixed-workload consolidation benchmark from VMware®.

Figure 1 : High Level Architecture of VMware Fault Tolerance

Environment Configuration :

•  VMware Fault Tolerance currently only supports 1 vCPU VMs and requires specific processors for enablement; for the purposes of our experimentation our VMmark Database and MailServer VMs were set to run with 1vCPU only.  For more information on FT and its requirements see here.
• VMmark is a benchmark intended to measure the performance of virtualization environments in an effort to allow customers to compare platforms.  It is also useful in studying the effect of architectural features. VMmark consists of six workloads (Web, File, Database, Java, Mail and Standby servers). Multiple sets of workloads (tiles) can be added to scale the benchmark load to match the underlying hardware resources. For more information on VMmark see here.

Test Methodology :

An initial performance baseline was established by running VMmark from 1 to 13 tiles on the primary system with Fault Tolerance disabled for all workloads. FT was then enabled for the MailServer and Database workloads after customer feedback suggested they were the applications most likely to be protected by FT. The performance tests were then executed a second time and compared to the baseline performance data.

Results :

The results in Table 1 are enlightening as to the performance and efficiency of VMware’s Fault Tolerance.  For this case, “FT-enabled Secondary %CPU”, indicates the total CPU utilized by the secondary system under test.  It should also be noted that, for our workload, the default ESX 4.0, High Availability, and Fault Tolerance settings were used and these results should be considered ‘out of the box’ performance for this configuration.  Finally, the secondary system’s %CPU is much lower by comparison to the primary system because it is only running the MailServer and Database workloads, as opposed to the six workloads that are being run on the primary system.

Table 1:

You can see that as we scaled both configurations toward saturation the overhead of enabling VMware Fault Tolerance remains surprisingly consistent, with an average delta in %CPU used of 7.89% over all of the runs.  ESX was also able to achieve very comparable scaling for both FT-enabled and FT-disabled configurations.  It isn’t until the FT-enabled configuration nears complete saturation, a scenario most end users will never see, that we start to see any real discernable delta in scores.

It should be noted that these performance and overhead statements may or may not be true for dissimilar workloads and systems under test.  From the results of our testing you can see that the advantage of having Mail servers and Database servers truly protected, without fear of end-user interruption, is completely justified.

It’s a tough world out there; you never know when the next earthquake, power outage, or someone tripping over a power cord will strike next.  It’s nice to know that your critical workloads are not only safe, but running at high efficiency.  The ability of VMware Fault Tolerance technology to provide quick and efficient protection for your critical workloads makes it a standout in the datacenter.

All information in this post regarding future directions and intent are subject to change or withdrawal without notice and should not be relied on in making a purchasing decision of VMware's products. The information in this post is not a legal obligation for VMware to deliver any material, code, or functionality. The release and timing of VMware's products remains at VMware's sole discretion.