Login phase

The login phase is where all users are logged into virtual desktops and they start running knowledgeworker tasks. The login phase for this test is set to 30 minutes. The figures below show the key PowerStore performance metrics during the login phase. 

Figure 5.   Login phase IOPS, bandwidth, and latency

PowerStore shows a steady and gradual increase in IOPS and bandwidth while maintaining submillisecond latency throughout the period. 

Figure 6.   Login phase CPU

PowerStore shows a steady and gradual increase in storage CPU utilization that peaked at 88% near the end of the login phase.

Figure 7.   Login phase IOPS detail

IOPS peaked at over 63,000 IO/s during the login phase. As expected, the percentage of read IOPS is higher than write IOPS during the login phase. During steady state, this ratio will reverse as shown below.

Figure 8.   Steady state IOPS, bandwidth, and latency

During steady state, demand for IOPS and bandwidth decreases and levels off, with an average latency of less than 0.4 milliseconds. 

Figure 9.   Steady state CPU

CPU demand is also less during steady state, averaging about 50%, with latency performance averaging less than 0.4 milliseconds. 

Figure 10.    Steady state bandwidth

The read/write ratio shows a higher percentage of writes during steady state. In this test, the data points in the call-out in Figure 10 show a sustained bandwidth of 74 MB/s reads and 423 MB/s writes. This result translates to an 18% read / 82% write ratio during steady state.  

Figure 11.    Refresh phase 

When a user logs off an instant clone VM, it is refreshed to match the current base image. In this test, Log in VSI logs off all 1,500 users at the end of the steady state in about 10 minutes. Figure 11 shows a period of increased I/O, bandwidth, and CPU demand on the PowerStore appliance as the refresh happens. Provisioning and refresh rates can be adjusted to lower the I/O and CPU demand. The trade-off is that it may take longer when provisioning new pools and for refreshes at logoff to complete. 

Although not shown here, defining a new Horizon instant clone VM pool also causes a similar period of high I/O, bandwidth, and CPU activity. When administrators plan for a successful VDI deployment using instant clones, a great user experience during the login phase and steady state are paramount considerations. However, the resource demands for VM pool creation and VM refresh at logoff can also be significant and must also be understood and factored in when sizing the environment.