After CPU, memory, and storage were allocated to the Exchange servers per the design considerations discussed earlier, LoadGen 2010 (v14.01.0139.000) was used to generate the 150 msg/day usage profile for the 8000 mailbox users in the large data center and the 1350 mailbox users in the small data center.
Note that the 150 msg/day profile translates to 181 tasks/day for each user, since each user executes tasks such as browsing the calendar in addition to sending and receiving E-mail messages. Each test run was configured to simulate a four-hour user day to generate peak periods of traffic when measuring server performance and memory utilization. Windows Performance Monitoring was run on each server role to monitor the performance counters recommended by Microsoft for monitoring Exchange performance.
When Windows Performance counters are used to monitor server performance in a VSphere VM, it is safe to assume that the results obtained are no more than 10% in error if CPU utilization stays below 80%. This is based on VMware guidance around performance testing Exchange 2010 available in their best practices documents
(http://www.vmware.com/solutions/business-critical-apps/exchange/resources.html). While Windows PerfMon graphs were captured in this solution for both physical and virtualized Exchange servers, it was verified that the VCenter performance graphs for VM CPU and memory utilization reported numbers similar to the PerfMon numbers.
The details of how to use Windows 2008 Performance Monitoring can be found at
http://technet.microsoft.com/en-us/library/cc770309(WS.10).aspx. Microsoft provides a list of the common and Exchange role-specific performance counters along with their acceptable thresholds:
Note The processor core megacycle values used to size this Exchange environment were estimated with hyperthreading disabled. Hyperthreading was left enabled by default on each UCS blade in this solution to yield potential higher CPU capacity.
Small DC
The backup Exchange VM for the Small DC that is located in the DR DC is assigned the same resources and is hosted on the same UCS blade hardware as the active Exchange VM in the Small DC. Therefore, after a site failover from the Small DC to the DR DC, it would demonstrate similar performance as that for the Small DC Exchange VM under normal operations.
The 1350 users of the Small DC are separated into two databases, so the LoadGen results at the end of a 10 hour test run, configured for a four-hour user day, show that each database of users got about a little more than 305,400 tasks. That is the expected number of tasks since there are 2.5 users days in a 10 hour period and, with each user configured for 181 tasks/user day, the expected total number of tasks is 2.5*181*675(users in each database) = 305,437.
Figure 61 LoadGen Report on 1350 Users for Small DC
The Exchange VM in the Small DC, which is configured with 32GB of RAM and 4 vCPU, hosts the 1350 active mailboxes and also hosts all three Exchange roles of Hub Transport, CAS, and Mailbox server.
Windows performance monitoring on this VM, as shown in Figure 62, confirms that 32GB is more than sufficient memory, since 2-3GB are available for use while the above-configured test is running. Average CPU utilization stays between 40-60%. Note that the CPU utilization on the AD/DNS stayed under 10%
with memory usage at around 1GB.
Figure 62 CPU and Memory Utilization on Small DC Exchange VM
The backup Exchange VM in the DR DC, shown as DRSmallAllRoles in the performance graph of Figure 63, has sufficient resources to support the log shipping and cluster communication with the Exchange VM in the Small DC. Average CPU utilization stays below 15% with occasional peaks under 40%. There are 2-3GB of memory available throughout the four-hour user day test.
Figure 63 CPU and Memory Utilization on DR DC Backup Exchange Server for Small DC
In addition to Windows Performance Monitoring, VCenter performance monitoring can be used to monitor CPU and memory utilization for a given VM. In the test with the Small DC 1350 active users, the VCenter performance chart for read latency on a RDM LUN containing a 675-user database can be monitored to ensure it stays below the Microsoft-recommended 50ms.
Figure 64 Disk Read Latency Reported by VCenter Performance Chart
Large DC
Under normal operations, the two physical mailbox servers in the Large DC each hosts 4000 active mailboxes and 4000 passive mailboxes. The physical mailbox server in the DR DC has a passive copy of all 8000 mailboxes. In Figure 65, the LoadGen test report shows that the expected number of user tasks were completed successfully. With 181 tasks generated for each user, 4000 users, and 2.5 user days (four-hour user day and 10 hours test duration), the total number of tasks configured and completed are 181*4000*2.5 = 1,810,000.
Figure 65 LoadGen Test Result for Large DC Normal Operations
With the above workload, CPU utilization as shown in Figure 66 stays around 32.7% on average. During the test, memory usage was monitored and it was found that about 9GB were left available, as shown in Figure 67. Both Hub Transport/CAS combined role VMs have enough CPU and memory to support 8000 mailbox users between them, as shown in Figure 66. Since CPU utilization spikes at the beginning of the LoadGen test on each HT/CAS VM, it is advisable to allocate two-four additional vCPUs to the remaining VM to handle all 8000 users if the other VM becomes unavailable.
Two AD/DNS VMs are sufficient to support the 8000 user workload. With each AD/DNS VM supporting a 4000 user population, it was observed that CPU utilization remained below 20% and about 2GB of RAM was left available after the 600MB NTDS.dit file, or the entire AD database, was cached in memory. There is plenty of headroom in the case where one AD/DNS VM fails and the other needs to take on all 8000 users.
Figure 66 CPU Utilization on Physical Mailbox Server for 4000 Large DC Users
Figure 67 Memory Available on Physical Mailbox Server for 4000 Large DC Users
Figure 68 CPU and Memory Utilization on a HT/CAS VM in Large DC for 4000 Active Users
Figure 69 CPU and Memory Utilization on AD/DNS in Large DC for 4000 Users
After a site failover from the Large DC to the DR DC, all 8000 users of the Large DC can be supported by the CPU and memory resources on the physical mailbox server in the DR DC. As the LoadGen test report in Figure 70 shows, the expected number of tasks have been executed over the 2.5 four-hour user days over a 10 hour test duration. Each user day involves 181 tasks executed, and given 8000 users, the total number of tasks is 2.5*181*8000 or 3,620,000.
Figure 70 LoadGen Test Results for Large DC Site Failover to DR DC
The performance graph in Figure 71 shows that CPU utilization on this DR mailbox server with the above workload averages around 60%. Over the course of this 10 hour test, there was at least 5GB of memory left available.
Figure 71 Performance of Physical Mailbox Server in DR DC After Site Failover