Configuring the Quality of Service (QoS) Timeout Setting

Configuring the Quality of Service (QoS) Timeout Setting

The Quality of Service Timeout (QoS timeout) setting plays an important role in governing failover member and arbiter behavior by defining the range of time, in milliseconds, that a mirror member waits for a response from another mirror member before taking action. The QoS timeout itself represents the maximum waiting time, while the minimum is one half of that. A larger QoS timeout allows the mirror to tolerate a longer period of unresponsiveness from the network or a host without treating it as an outage; decreasing the QoS allows the mirror to respond to outages more quickly. Specifically, the QoS timeout affects the following situations:

• If the backup failover member does not acknowledge receipt of data from the primary within the range defined by the QoS timeout, the primary disconnects the backup and acts in accord with a possible outage of the backup.

• If the backup receives no message from the primary within the range defined by the QoS timeout, the backup disconnects and acts in accord with a possible outage of the primary.

• If the arbiter does not receive a response from a failover member within the range defined by the QoS timeout, it considers its connection with that failover member to be lost.

• If operations performed on a failover member’s host cause the host to be entirely unresponsive for a period within the range defined by the QoS timeout, unwanted failover or alerts may result. This is a particular concern where virtualization platform operations such as backup or migration are involved; see Mirroring in a Virtualized Environment for more information

See Automatic Failover Mechanics for complete and detailed information about the role the QoS timeout plays in the behavior of the failover members and the arbiter.

The default QoS is 8 seconds (8000 ms) to allow for several seconds of intermittent unresponsiveness that may occur on some hardware configurations. Typically, deployments on physical (nonvirtualized) hosts with a dedicated local network can reduce this setting if a faster response to outages is required.

The Quality of Service Timeout setting can be adjusted on the Create Mirror page or the primary failover member’s Edit Mirror page.