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Power Management and Performance in VMware vSphere 5.1 and 5.5

Power consumption is an important part of the datacenter cost strategy. Physical servers frequently offer a power management scheme that puts processors into low power states when not fully utilized, and VMware vSphere also offers power management techniques. A recent technical white paper describes the testing and results of two performance studies: The first shows how power management in VMware vSphere 5.5 in balanced mode (the default) performs 18% better than the physical host’s balanced mode power management setting. The second study compares vSphere 5.1 performance and power savings in two server models that have different generations of processors. Results show the newer servers have 120% greater performance and 24% improved energy efficiency over the previous generation.

For more information, please read the paper: Power Management and Performance in VMware vSphere 5.1 and 5.5.

Power Management and Performance in ESXi 5.1

Powering and cooling are a substantial portion of datacenter costs. Ideally, we could minimize these costs by optimizing the datacenter’s energy consumption without impacting performance. The Host Power Management feature, which has been enabled by default since ESXi 5.0, allows hosts to reduce power consumption while boosting energy efficiency by putting processors into a low-power state when not fully utilized.

Power management can be controlled by the either the BIOS or the operating system. In the BIOS, manufacturers provide several types of Host Power Management policies. Although they vary by vendor, most include “Performance,” which does not use any power saving techniques, “Balanced,” which claims to increase energy efficiency with minimal or no impact to performance, and “OS Controlled,” which passes power management control to the operating system. The “Balanced” policy is variably known as “Performance per Watt,” “Dynamic” and other labels; consult your vendor for details. If “OS Controlled” is enabled in the BIOS, ESXi will manage power using one of the policies “High performance,” “Balanced,” “Low power,” or “Custom.” We chose to study Balanced because it is the default setting.

But can the Balanced setting, whether controlled by the BIOS or ESXi, reduce performance relative to the Performance setting? We have received reports from customers who have had performance problems while using the BIOS-controlled Balanced setting. Without knowing the effect of Balanced on performance and energy efficiency, when performance is at a premium users might select the Performance policy to play it safe. To answer this question we tested the impact of power management policies on performance and energy efficiency using VMmark 2.5.

VMmark 2.5 is a multi-host virtualization benchmark that uses varied application workloads as well as common datacenter operations to model the demands of the datacenter. VMs running diverse application workloads are grouped into units of load called tiles. For more details, see the VMmark 2.5 overview.

We tested three policies: the BIOS-controlled Performance setting, which uses no power management techniques, the ESXi-controlled Balanced setting (with the BIOS set to OS-Controlled mode), and the BIOS-controlled Balanced setting. The ESXi Balanced and BIOS-controlled Balanced settings cut power by reducing processor frequency and voltage among other power saving techniques.

We found that the ESXi Balanced setting did an excellent job of preserving performance, with no measurable performance impact at all levels of load. Not only was performance on par with expectations, but it did so while producing consistent improvements in energy efficiency, even while idle. By comparison, the BIOS Balanced setting aggressively saved power but created higher latencies and reduced performance. The following results detail our findings.

Testing Methodology
All tests were conducted on a four-node cluster running VMware vSphere 5.1. We compared performance and energy efficiency of VMmark between three power management policies: Performance, the ESXi-controlled Balanced setting, and the BIOS-controlled Balanced setting, also known as “Performance per Watt (Dell Active Power Controller).”

Configuration
Systems Under Test: Four Dell PowerEdge R620 servers
CPUs (per server): One Eight-Core Intel® Xeon® E5-2665 @ 2.4 GHz, Hyper-Threading enabled
Memory (per server): 96GB DDR3 ECC @ 1067 MHz
Host Bus Adapter: Two QLogic QLE2562, Dual Port 8Gb Fibre Channel to PCI Express
Network Controller: One Intel Gigabit Quad Port I350 Adapter
Hypervisor: VMware ESXi 5.1.0
Storage Array: EMC VNX5700
62 Enterprise Flash Drives (SSDs), RAID 0, grouped as 3 x 8 SSD LUNs, 7 x 5 SSD LUNs, and 1 x 3 SSD LUN
Virtualization Management: VMware vCenter Server 5.1.0
VMmark version: 2.5
Power Meters: Three Yokogawa WT210

Results
To determine the maximum VMmark load supported for each power management setting, we increased the number of VMmark tiles until the cluster reached saturation, which is defined as the largest number of tiles that still meet Quality of Service (QoS) requirements. All data points are the mean of three tests in each configuration and VMmark scores are normalized to the BIOS Balanced one-tile score.

Effects of Power Management on VMmark 2.5 score

The VMmark scores were equivalent between the Performance setting and the ESXi Balanced setting with less than a 1% difference at all load levels. However, running on the BIOS Balanced setting reduced the VMmark scores an average of 15%. On the BIOS Balanced setting, the environment was no longer able to support nine tiles and, even at low loads, on average, 31% of runs failed QoS requirements; only passing runs are pictured above.

We also compared the improvements in energy efficiency of the two Balanced settings against the Performance setting. The Performance per Kilowatt metric, which is new to VMmark 2.5, models energy efficiency as VMmark score per kilowatt of power consumed. More efficient results will have a higher Performance per Kilowatt.

Effects of Power Management on Energy Efficiency

Two trends are visible in this figure. As expected, the Performance setting showed the lowest energy efficiency. At every load level, ESXi Balanced was about 3% more energy efficient than the Performance setting, despite the fact that it delivered an equivalent score to Performance. The BIOS Balanced setting had the greatest energy efficiency, 20% average improvement over Performance.

Second, increase in load is correlated with greater energy efficiency. As the CPUs become busier, throughput increases at a faster rate than the required power. This can be understood by noting that an idle server will still consume power, but with no work to show for it. A highly utilized server is typically the most energy efficient per request completed, which is confirmed in our results. Higher energy efficiency creates cost savings in host energy consumption and in cooling costs.

The bursty nature of most environments leads them to sometimes idle, so we also measured each host’s idle power consumption. The Performance setting showed an average of 128 watts per host, while ESXi Balanced and BIOS Balanced consumed 85 watts per host. Although the Performance and ESXi Balanced settings performed very similarly under load, hosts using ESXi Balanced and BIOS Balanced power management consumed 33% less power while idle.

VMmark 2.5 scores are based on application and infrastructure workload throughput, while application latency reflects Quality of Service. For the Mail Server, Olio, and DVD Store 2 workloads, latency is defined as the application’s response time. We wanted to see how power management policies affected application latency as opposed to the VMmark score. All latencies are normalized to the lowest results.

Effects of Power Management on VMmark 2.5 Latencies

Whereas the Performance and ESXi Balanced latencies tracked closely, BIOS Balanced latencies were significantly higher at all load levels. Furthermore, latencies were unpredictable even at low load levels, and for this reason, 31% of runs between one and eight tiles failed; these runs are omitted from the figure above. For example, half of the BIOS Balanced runs did not pass QoS requirements at four tiles. These higher latencies were the result of aggressive power saving by the BIOS Balanced policy.

Our tests showed that ESXi’s Balanced power management policy didn’t affect throughput or latency compared to the Performance policy, but did improve energy efficiency by 3%. While the BIOS-controlled Balanced policy improved power efficiency by an average of 20% over Performance, it was so aggressive in cutting power that it often caused VMmark to fail QoS requirements.

Overall, the BIOS controlled Balanced policy produced substantial efficiency gains but with unpredictable performance, failed runs, and reduced performance at all load levels. This policy may still be suitable for some workloads which can tolerate this unpredictability, but should be used with caution. On the other hand, the ESXi Balanced policy produced modest efficiency gains while doing an excellent job protecting performance across all load levels. These findings make us confident that the ESXi Balanced policy is a good choice for most types of virtualized applications.

Exploring Generational Differences in Performance and Energy Efficiency Using VMware VMmark 2.5

Each new generation of servers brings advances in hardware components. For IT professionals purchasing or managing new generations of hardware, it’s vital to understand how these incremental hardware improvements translate into real-world gains in the datacenter. Using the VMware VMmark 2.5 virtualization benchmark, we compared performance and energy efficiency of two different generations of servers in four-node clusters.

VMmark 2.5 is a multi-host virtualization benchmark that uses varied application workloads as well as common datacenter operations to model the demands of the datacenter. VMs running diverse application workloads are grouped into units of load called tiles. For more details, see the VMmark 2.5 overview.

Testing Methodology
All tests were conducted on two four-node clusters running VMware vSphere 5.1. We compared performance and energy efficiency between a cluster of previous generation Dell R310 servers, and a cluster of current generation Dell R620 servers. For simplicity, we refer to these as the ‘old cluster’ and ‘new cluster,’ respectively. Among other hardware differences, the old cluster servers contained four-core Intel Nehalem processors while the new cluster servers contained eight-core Intel Sandy Bridge EP processors. Memory in the newer servers was appropriately scaled up to accommodate their increased processing power and represents common current server configurations. Software and storage configurations were identical between clusters.

Configuration
Old Cluster
Systems Under Test: Four Dell PowerEdge R310 servers
CPUs (per server): One Quad-Core Intel® Xeon® X3460 @ 2.8 GHz, Hyper-Threading enabled
Memory (per server): 32GB DDR3 ECC @ 800 MHz

New Cluster
Systems Under Test: Four Dell PowerEdge R620 servers
CPUs (per server): One Eight-Core Intel® Xeon® E5-2665 @ 2.4 GHz, Hyper-Threading enabled
Memory (per server): 96GB DDR3 ECC @ 1067 MHz

Storage Array: EMC VNX5700
        62 Enterprise Flash Drives (SSDs), RAID 0, grouped as 3 x 8 SSD LUNs, 7 x 5 SSD LUNs, and 1 x 3 SSD LUN
Hypervisor: VMware vSphere 5.1.0
Virtualization Management: VMware vCenter Server 5.1.0
VMmark version: 2.5

Results
To determine the maximum VMmark load the old cluster could support, we increased the number of VMmark tiles until the cluster reached saturation, which is defined as the largest number of tiles that still meet Quality of Service (QoS) requirements. We then tested the new cluster at the same number of tiles. All data points are the mean of four tests in each configuration and VMmark scores are normalized to the old cluster’s performance.

The new cluster had a 32% higher VMmark score in combination with a 41% lower CPU utilization. The new cluster also showed a 24% increase in energy efficiency over the old cluster, which we’ll discuss further below. At four tiles, the old cluster was bottlenecked on CPU, resulting in decreased workload throughput, while the new cluster was not. With CPU resources to spare, the new cluster met the requested load at lower latencies, which increased its total throughput and score. Mean I/O latencies remained low for both clusters at 1.2ms reads and 1.1ms writes for the old cluster and 1.0ms reads and 0.9ms writes for the new cluster.

We next determined the maximum VMmark load the new cluster could support. While the old cluster was saturated at four tiles, the new cluster accommodated more than twice the load at nine tiles and produced a score 120% higher than the old cluster. Mean I/O latencies remained low at 1.0ms.

Click to enlarge

The performance advantages of the R620 over the R310 were largely due to the generational improvements of the R620’s eight-core E5-2665 processor versus the R310’s four-core x3460 processor, which includes improved bus speeds and larger L3 cache, and the R620’s increased memory.

These performance results suggest that it would be possible to replace four Dell R310 servers with two Dell R620 servers and expect better than equivalent performance. We put this to the test by removing two nodes from the new cluster and found that the two remaining nodes did support four tiles at 93% utilization, with an 11% higher VMmark score and 74% greater energy efficiency than the four-host old cluster.

Beyond their raw performance capability, we also compared the two server generations on their energy efficiency. The Performance per Kilowatt metric, which is new to VMmark 2.5, models energy efficiency as VMmark score per kilowatt of power consumed. Below, we’ve plotted energy efficiency against the normalized VMmark score. Both clusters were run with their servers’ power management set to “maximum performance.”

Energy Efficiency as a Function of VMmark 2.5 Score

Two trends emerge from this figure. First, at four tiles, the four-host new cluster accomplishes more work at higher energy efficiency than the old cluster. Across the board, the new cluster is more energy efficient than the old cluster. Second, within the four-host new cluster, greater energy efficiency is correlated with increase in VMmark score. As the CPUs become busier, performance increases at a faster rate than the required power. This can be understood by noting that an idle server will still consume power, but with no performance to show for it. A highly utilized server is typically the most energy efficient per request completed, which is confirmed by the two-host new cluster that achieved high efficiency at 93% utilization. Higher energy efficiency creates cost savings in energy consumption and in cooling costs.

Our investigation shows that, while running vSphere 5.1, two newer Dell R620 servers are capable of supporting a greater load than four older Dell R310 servers. Because the Dell R620 performance is more than double that of the Dell R310, a four-node Dell R620 cluster reached a 120% higher maximum score than the Dell R310 cluster. In addition to its performance advantages, at each load level the Dell R620 cluster performed with greater energy efficiency, showing that the Dell R620 has superior performance but also has greater energy efficiency than the Dell R310.