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Increase VM Density

Increase VM Density

Increase VM Density

Storage IO bottleneck is one of the key reason preventing larger number of VMs from being deployed on ESXi hosts. VirtuCache can substantially improve VM density by increasing storage IOPS and reducing latencies.

Depending on the workload, size of the SSD, and performance characteristics of the SSD (e.g. whether it is SATA, SAS or PCIe), VirtuCache can increase VM density by between 2-6X.

Use Case at MBTI

MBTI is in the business of assessing and improving the performance of people and organizations. They are best known for Myers-Briggs tests, the world’s foremost personality assessment tests used by institutions to help employees better understand themselves and how they interact with others.

MBTI Server and Storage Infrastructure

MBTI’s IT department had four physical servers running Windows Server VMs on VMware 5.1. Before VirtuCache, there were about 80 VMs running MS Exchange, MS Dynamics, Unidesk, App Assure, and other enterprise applications, equally distributed between these 4 physical hosts.
Storage – A total of 18 TB of storage on LUNs on a gigabit iSCSI Hitachi storage appliance was used by these servers.

Workload Characteristics

On an average, less than 4 TB of data changed every day and read-write mix varied widely between 40-60 to 80-20 read-write ratio.
VMware’s Distributed Resource Scheduler (DRS) functionality was configured to be automatic and aggressive, which ensured that workloads were equally distributed at all times across these 4 physical hosts.

VirtuCache Deployment

VirtuCache along with a PCIe Flash card was installed in the ESXi hosts on MBTI Servers.

Steady state Cache Hit Ratio (ratio of IO served from the in-server SSD to the IO served from backend LUNs) was at 75-80%, with warm-up time of 10 minutes.

Guest Average Latency (GAVG) was measured before and after VirtuCache, using VMware esxtop. The below table shows reduced GAVG after deploying VirtuCache, which consequently also resulted in higher VM densities. Since auto-DRS was enabled on the VMware cluster, VMware automatically sensed improvements in storage performance on the server that had VirtuCache installed and moved VMs from the other 3 servers to this server, increasing the number of VMs of the host from 20 before VirtuCache to 42 after VirtuCache.

Guest Average Latencies (GAVG) Before VirtuCache After VirtuCache
Read GAVG 35-1500 ms 0.1 – 6 ms
Write GAVG 20 – 600 ms 0.1 – 6 ms

Benefit to MBTI

Using VirtuCache, MBTI was able to reduce the number of physical servers in their VMware cluster from four to two, thus reducing VMware licensing costs, rack space and hardware costs.

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