For XenApp Power and Capacity Management, capacity is expressed as a number of sessions (or session count).
The XenApp servers being managed by Power and Capacity Management are called a farm. This farm may include some or all of the servers in a XenApp farm, or it may contain XenApp servers from different XenApp farms (for example, in a XenApp farm that covers multiple sites, you might have a Power and Capacity Management farm for the XenApp servers in each site). The Power and Capacity Management farm name is distinct from the XenApp farm name.
You define a workload, which is a logical grouping of servers that all host the same application or set of applications. (In XenApp terms, this is referred to as an application silo.) You use setpoints to control how servers are power managed and how load is consolidated within the workload.
Use Power and Capacity Management to observe and record utilization and capacity levels. Console monitoring and report generation provide valuable information, regardless of whether or not you enable power management and load consolidation.
The concentrator, database, reporting, and management console components are referred to as administration components.
|Online session reserve||Infinite; all servers are kept online. The management console displays this value as an infinity symbol.|
|Minimum session capacity||Zero, which is equivalent to unset.|
|Maximum session capacity||infinite, which is equivalent to unset; the management console displays this value as an infinity symbol.|
|Minimum available servers||Zero, which is equivalent to unset.|
You specify setpoints in a workload schedule. Set the secondary optimal load value in global configuration settings.
The system attempts to meet the online session reserve setpoint first. It then bounds the output using the minimum and maximum session capacity setpoints. Finally, the system checks and ensures that the resulting number of online servers meets the minimum available servers setpoint.
A schedule usually specifies the online session reserve and the minimum available servers setpoints.
After you initially set the online session reserve and minimum available servers setpoint values with scheduled changes throughout the day, observe server and session activity, and then fine-tune the schedule and setpoint values to optimize server capacity and use.
After you enable a workload for power management, you can manually override the schedule with different setpoint values.
For example, a manual override can be useful when there is an unexpected surge in demand on the XenApp workload that is likely to continue for a few hours. Instead of changing the schedule, you can initiate an override. When the surge has subsided and the normal conditions have returned, you can cancel the override, and the scheduled setpoint values are reapplied.
Using a manual override can be helpful when the schedule requires attention or maintenance.
Manual override differs from disabling power management. During a manual override, power management is still active, but the setpoints are controlled by the administrator instead of the schedule. Disabling power management for a workload is equivalent to turning off the Power and Capacity Management feature for that workload.
In a server profile, you can also specify a power action timeout value, which is used when a power off or power on control is issued. If the operation does not complete successfully before the timer expires, Power and Capacity Management assumes the operation failed.
If the hardware configuration changes (for example, more RAM is added to a server), Power and Capacity Management creates a new profile. (The original profile is not altered, because other servers may still be using it. Also, when a hardware change occurs, server capacity can change.)
As new servers connect and report their profiles, they inherit any existing configured capacity value if they have the same profile as an existing configured server.
The control mode affects whether the server is eligible for power management or participating in load consolidation.
Set the server control mode for existing servers in server properties, and for new servers in global configuration settings.
You can install a Power and Capacity Management concentrator on two servers. This concentrator cluster has a master-slave relationship; one concentrator is the master and the other is a slave. All connections from agents on the XenApp servers go to the current master concentrator; there is no load balancing among multiple concentrators.
Concentrators negotiate for mastership and monitor the health of the current master via the database. If the current master stops updating the database, the slave concentrator becomes the master. Failover usually occurs within 60 seconds.
You can explicitly force a running slave concentrator to become the master concentrator. This may be necessary when a master concentrator has planned maintenance.
Each concentrator registers an Active Directory Service Connection Point (SCP) under the machine account where the concentrator is installed and records an entry in the database. When the agent on the XenApp server starts, it queries the SCP to discover all known concentrators. Each agent then tries to connect to each concentrator, looking for the master. The management console also performs the same discovery process and connection attempts.
To change the port the agent uses to communicate with the concentrator (the default port is 11168), edit the PCMConcentrator.exe.config file in the Install directory, then restart the PCM Concentrator service.
Power and Capacity Management uses virtual machine management to automatically locate virtual machines it manages; therefore, you do not need to manually configure associations between the virtual machines and their managing XenServer hosts.
Virtual machine management supports multiple concurrent XenServer resource pools. The concentrator automatically connects to the XenServer resource pool, and periodically queries the inventory of virtual machines. The management console displays the inventory poll results as a count of the number of virtual machines. The concentrator continually updates the results.
If you move a virtual machine image from one XenServer resource pool to another, Power and Capacity Management learns about this during its inventory polling.
Dynamic Capacity Estimation calculates individual server capacities based on the load on each server. This enables the capacity of each server to more accurately reflect the actual number of sessions it is capable of handling.
The load on each server is determined by its assigned XenApp load evaluator. The assigned evaluator(s) should therefore be configured so that the desired load criteria are taken into account. The Power and Capacity Management agent regularly monitors the load and updates the estimated capacity on its server accordingly.
Depending on the load, the estimation may determine that a server is capable of holding more sessions than the configured typical capacity. To allow the dynamic capacity estimation to set capacities higher than the typical value, you can set the estimated capacity limit to any value higher than the typical capacity.
When Power and Capacity Management determines a power on or power off operation is required, it considers a server's power controller preference (and site preference, for XenApp servers installed on XenServer virtual machines). For a power on operation, the selection algorithm chooses a server with a higher power controller preference before a server with a lower preference. For a power off operation, the algorithm chooses a server with a lower power controller preference before a server with a higher preference. Configure power controller preference in server properties. For best practice, specify the preference of more power-efficient servers higher than older, less power-efficient servers.
When Power and Capacity Management selects a XenApp server for power off and that server is currently hosting sessions, the server is placed into drain mode. While in drain mode, a server does not accept new sessions, but allows reconnection of disconnected sessions. (In meeting capacity setpoints, Power and Capacity Management ignores the load from servers that are currently draining or powering off, as well as servers currently being evaluated for draining/power off.) A server in drain mode powers off only when no sessions remain. If the agent loses connection to the concentrator, the agent reverts drain mode on draining servers and reenables logons.
When Power and Capacity Management issues a power off or power on control, a timer starts (set the value of this timer in the server profile). If the operation does not complete successfully before the timer expires, Power and Capacity Management reports the operation failed. The management console displays power control operation failures. When a power control operation completes successfully, all control errors associated with that server are cleared.
You can enable or disable power management on a global and per-workload basis. The global setting overrides the per-workload setting. When you disable power management for a workload, any servers currently in drain mode are reverted out of drain mode.
Load consolidation has the opposite effect to traditional XenApp load balancing. It aims to consolidate sessions onto fewer servers instead of spreading load evenly across many servers. By consolidating sessions, there is greater opportunity to power down excess servers, saving power and reducing running costs. Greater consolidation of sessions equates to higher levels of utilization per server while online.
Load consolidation works by continually monitoring the number of active sessions and remaining capacity for each server. It aims to load up small groups of servers with new sessions to a level that the servers are comfortable with handling. In Power and Capacity Management, this level is called the optimal load. Once a server reaches optimal load, load consolidation will enable an additional server in the workload to accept new session load. When used in conjunction with Power Management, this additional server will be powered on automatically if it is currently powered off.
The optimal load is a configurable value expressed as a percentage, with a default value of 70%. That is to say, load consolidation will add sessions to a server until it reaches or exceeds 70% of full server capacity. The remaining 30% of capacity acts as a buffer to ensure existing sessions on the server have spare computing resources to work with. You can tune the optimal load threshold to find the right balance between performance and utilization.
For load consolidation to work effectively, the capacity level of each server needs to be measured. Because the remaining capacity can change as load on the server fluctuates, capacity levels need to be continually re-evaluated. This is the role of dynamic capacity estimation.