Time synchronization using NTP

The Network Time Protocol (NTP) client must be used in the Db2® Mirror environment to keep the system clocks synchronized. The two Db2 Mirror nodes also must use the same local time and time zone.

There are three options for configuring time synchronization for Db2 Mirror:

External time server: Both nodes reference the same external time server.
Chained time server: The setup source node references an external time server.; The setup copy node references the setup source node.
Peer time server: The setup copy node references the setup source node.

For more information about NTP, see ADD_TIME_SERVER procedure and NTP client.

Note: If you are currently using the Simple Network Time Protocol (SNTP) client to keep your system clock synchronized, be aware that the SNTP and NTP clients cannot run simultaneously. The time adjustment system value (QTIMADJ) is set to QIBM_OS400_SNTP when the SNTP client starts or QIBM_OS400_NTP when the NTP client starts.

Note: If you plan to specify more than one external NTP time server, you should not use two or three preferred NTP time servers; four NTP servers is the recommended minimum. The reason for this is that when NTP gets information from two or three time sources and the times provided do not fall into a small enough range, the NTP client cannot determine which time source is correct.

Note: To ensure the system clocks stay synchronized, even while powered down, it is recommended to configure a Time Reference Partition on your POWER® servers. For more information about Time Reference Partitions, see Time and Date Management with PowerVM®.

External time server

The external time server configuration option has both Db2 Mirror nodes reference the same time server as shown below.

Each node will independently check and adjust to the time supplied by the external time server and thus remain synchronized with each other. The time server could be a server within your local network or a public time server. The time server should be accessible through a reliable and low latency network link to minimize jitter. A local network time server is highly recommended.

Chained time server

The chained time server configuration option configures the setup source node to reference an external time server and the setup copy node references the setup source node as the preferred time server.

The setup source node will be configured as an SNTP server.

The external time server could be a server within your local network or it could be a public time server. As mentioned before, the external time server should ideally be accessible through a reliable and low latency network link to minimize jitter, so a site time server is highly recommended.

As shown in the configuration below, the NTP client on the setup copy node will be configured to also reference the external time server as a non-preferred server. It will automatically failover to synchronize directly with the external time server when the setup source node is unavailable as the preferred time server.

Peer time server

The peer time server configuration option configures the setup copy node to reference the setup source node as the preferred time server.

The setup source node will be configured as an SNTP server.

As shown in the configuration below, this option uses no external time servers.