On an IBM z16 mainframe, precise timekeeping isn’t just a convenience; it’s critical for data consistency, logging accuracy, and workload coordination, especially in environments like Parallel Sysplex. The key technology that makes this possible is Server Time Protocol (STP).

The Role of STP

STP establishes a Coordinated Timing Network (CTN), ensuring every Central Processor Complex (CPC) in the network operates on a single, shared clock known as Coordinated Server Time (CST). Within the CTN:

• Preferred Time Server (PTS) – The primary, authoritative time source.
• Backup Time Server (BTS) – A hot standby ready to assume the PTS role if needed.
• Arbiter – A neutral tie-breaker that helps resolve disputes if the PTS becomes unavailable or if a switchover is required.

If the PTS fails or is taken offline, the BTS seamlessly takes over with the Arbiter’s assistance, keeping all systems synchronized.

Stratum Levels

To maintain order and prevent timing loops, STP uses Stratum Levels:

• Stratum 1 – The highest-accuracy source (typically the PTS).
• Stratum 2 – Systems directly synchronized with Stratum 1 (such as the BTS and Arbiter).
• Stratum 3 and below – Additional CPCs or LPARs that derive their time from Stratum 2 servers.

This hierarchy ensures a clean, predictable flow of time distribution across the network.

HMC as the Control Center

The Hardware Management Console (HMC) provides the interface to configure and monitor STP. From the HMC you can:

• Create and manage CTNs, assign PTS/BTS/Arbiter roles, and perform planned switchovers.
• Enable Network Time Protocol (NTP) to synchronize the HMC’s own clock with an external time source or allow the HMC to act as an NTP server.
• Adjust settings during maintenance or after CPC resets to keep the entire environment aligned.

By leveraging STP’s hierarchical design and managing it through the HMC, IBM mainframes maintain precise, fault-tolerant time synchronization—protecting data integrity and ensuring consistent performance across the enterprise.