December 11, 2012
UCLA has deployed Virtual Desktops for students and staff using VMware Horizon View.
End users of these virtual desktops complained about slow boot times, Windows cursor and start button freezing and generally slow response times from the virtual desktops at various times during the day.
To better understand the root cause of these issues, we collected VM level read and write storage throughput and latency data using VMware esxtop. Both read and write throughput were always under 5 MBps, and write latencies were always less than 20 ms. It was the read latencies that would peak to 100 ms at various times during the day. Also the Trend Micro Deep Security Anti-Virus VM would lock up files during a file scanning operation resulting in a sudden jump in latencies across all the VMs on the host.
VMware Horizon View 5.1 was deployed on HP BL490c Gen7 blades with 98 GB RAM.
Linked clones were used for virtual desktop VMs. Both user data and parent images were stored on 18 TB of LUN capacity provisioned on 8 gbps Xiotech and HP EVA appliances.
VirtuCache was deployed on each of the physical hosts with commodity Seagate SATA SSDs (cost of SSD $1 / GB). We would have preferred to use the lower latency SAS SSDs, however since the onboard RAID controller on the blades could only support SATA, we could use only SATA SSDs.
VirtuCache was configured to cache LUNs on the HP EVA and Xiotech appliances to a single 480 GB Seagate 600 Pro SATA SSDs installed in each of the 6 ESXi hosts.
The ratio of cache capacity (SSD capacity in the host) to disk space utilization on the LUNs by the host was 16%.
To compare VM level latencies before and after VirtuCache, esxtop was used in batch mode to export data to flat file that was subsequently processed in excel to generate the chart below.
The chart below shows maximum latencies before and after VirtuCache for each of the VMs on the host for two consecutive Mondays. Performance data for the ESXi host shown in this graph is a representative example of the extent to which the performance of each host in the cluster was improved.
Benefit to UCLA
By using VirtuCache with a single 480 GB Seagate enterprise SATA SSD, peak VM level latencies were reduced by a fourth or less. We ensured that maximum VM latency at all times remained under 20 milliseconds.