6.12 What are Server Pool Policies?

Managing load and reducing power consumption are two of the major benefits of virtualization. When a server is already under significant load, it is preferable to distribute the virtual machines that it is running across less utilized servers within the server pool. Equally, during periods of low utilization it is preferable to consolidate virtual machines across as few servers as possible so that unused servers can be powered off to reduce energy consumption.

Oracle VM provides a facility to handle this kind of behavior automatically. This facility is handled by creating a server pool policy. Server pool policies allow you to define the different options that you wish to support. These are defined as follows:

It is also possible to apply these policies to the networks that are available within a server pool, by setting network utilization thresholds that trigger these behaviors within the server pool. This is discussed in more detail in Section 6.12.3, “DRS/DPM Network Policies”.

If you have set the inbound migration lock feature to disallow new virtual machines on an Oracle VM Server, then any server pool policies you set are restricted from migrating virtual machines, or creating new ones on the server. See Section 7.12, “How Can I Protect Virtual Machines?” for more information on using the inbound migration lock feature.

All Oracle VM Servers must have matching release numbers for either of these server pool policies to be effective. If the release numbers for Oracle VM Servers do not match for a significant length of time, virtual machines running on Oracle VM Servers with higher release numbers are unable to live migrate to Oracle VM Servers with lower release numbers. These policies perform a check before attempting a migration and will prevent the migration in the event that the target server does not have a matching release number. Therefore, in an environment with mixed server versions, server pool policies may not be implemented.

6.12.1 Distributed Resource Scheduler (DRS)

The Distributed Resource Scheduler (DRS) optimizes virtual machine resource utilization in a server pool. DRS automatically moves running virtual machines to another Oracle VM Server in a server pool if any of the Oracle VM Servers exceed a specified CPU threshold for a specified period of time. DRS continuously samples performance data from every Oracle VM Server and every virtual machine.

The movement of virtual machines is policy-driven. When a threshold is reached, Oracle VM Manager live migrates the running virtual machine from one Oracle VM Server to another, without down time. Oracle VM Manager allows you to specify a DRS threshold for each server pool, and to choose which Oracle VM Servers participate in the policy.

See Define or Edit Server Pool Policies in the Oracle VM Manager User's Guide for information on enabling and configuring the DRS in a server pool.

In addition, you can define the default start-up policy for all of your virtual machines at the server pool level. The default VM start policy is Best Server, which determines VM placement based on DRS and DPM algorithms. As of Release 3.4.5, a new VM start policy option named Balance Server is available, which optimizes the CPU and memory utilization across the servers in a pool. It is possible to override the default policy within the configuration of each virtual machine.

See Create Server Pool in the Oracle VM Manager User's Guide for additional information on VM start policies.

6.12.2 Distributed Power Management (DPM)

Distributed Power Management (DPM) is used when there are periods of relative low resource utilization to increase the consolidation ratio on fewer Oracle VM Servers. DPM dynamically migrates virtual machines from under-utilized Oracle VM Servers. When there are Oracle VM Servers without virtual machines running the Oracle VM Server can be powered off, conserving power until the Oracle VM Server is needed again.

DPM aims to keep only the minimum necessary number of Oracle VM Servers running. If a periodic check reveals that a Oracle VM Server's CPU utilization is operating at below a user-set level, virtual machines are live migrated to other Oracle VM Servers in the same server pool.

When all virtual machines are migrated, the Oracle VM Server is shut down.

If an Oracle VM Server exceeds the DPM policy CPU threshold, Oracle VM Manager looks for other Oracle VM Servers to migrate virtual machines to from the busy Oracle VM Server. If no powered Oracle VM Servers are available, Oracle VM Manager finds and starts an Oracle VM Server using its Wake-On-LAN capability. When that Oracle VM Server is running, Oracle VM Manager off-loads the virtual machines from the busy Oracle VM Server to the newly started Oracle VM Server to balance the overall load. It is a prerequisite that all the servers that participate in DPM have Wake-On-LAN enabled in the BIOS for the physical network interface that connects to the dedicated management network.

Oracle VM Manager allows you to specify a DPM threshold for each server pool, and to choose which Oracle VM Servers participate in the policy.

See Define or Edit Server Pool Policies in the Oracle VM Manager User's Guide for information on enabling and configuring DPM in a server pool.

6.12.3 DRS/DPM Network Policies

Both the DRS and DPM policies can also be set for the networks used by Oracle VM Servers in a server pool. When a network used by an Oracle VM Server exceeds its threshold, virtual machines are migrated to other Oracle VM Servers to either balance the resources used (DRS), or reduce the power used (DPM). Each network on an Oracle VM Server can have a threshold set. The threshold applies to either the received data or the transmitted data. If the threshold is set to say 50%, when an Oracle VM Server's receive or transmit traffic on that network exceeds 50% of the theoretical capacity of the network, the Oracle VM Server is deemed to be over the threshold. The theoretical capacity of a network on an Oracle VM Server is equal to the port speed of the physical Ethernet adapter on the Oracle VM Server. If the network is bonded in a fail-over configuration, then the port capacity is equal to the port speed of one of the Ethernet adapters. If the network is bonded on a Oracle VM Server with link aggregation, then the network capacity is equal to the sum of the speed of the bonded Ethernet adapters.

You set the network policies for DRS and DPM when you set up the server pool policy. See Define or Edit Server Pool Policies in the Oracle VM Manager User's Guide for information on enabling and configuring network DRS and DPM policies in a server pool.

It is important to understand that a network policy can be defined for a server pool, even if that network is not used by any servers in the server pool. In this case, the policy is simply ignored, however if a server with the network attached is added to the server pool at a later date, the policy is automatically enabled for the network attached to that server. If you define a network policy on a server pool and later remove all of the servers that had that network attached, the policy still remains enforced on the server pool. Therefore, it is always good practice to regularly check the server pool policy when adding servers to a server pool, since an old policy may be in place that affects the behavior of the network.