Data Domain: How to verify Data Domain OS Readiness for Leap Second Event

Summary: This knowledge base article addresses Data Domain OS compatibility and readiness for leap second events. It also covers frequently asked questions that have been verified to ensure proper handling of leap second adjustments within Data Domain environments. ...

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Instructions

Below are the more frequently asked questions that have been verified by engineering for handling of Leap Second Events for Data Domains: 

  • System Stability
    • Question: Are there any known issues where the leap-second flag from an NTP server causes a kernel stop responding or high utilization in this Data Domain OS version?
    • Answer: No known issues have been identified. Engineering has not observed any historical problems related to leap second events causing instability. Also, the Data Domain OS runs on the Linux 5.4 kernel, which includes fixes for earlier leap second-related kernel stop responding issues.
  • Time Synchronization Method
    • Question: Does Data Domain OS support "Time Smearing" from a source NTP server, or does it require a hard "step" adjustment?
    • Answer: Data Domain OS supports both time smearing and hard step adjustments. Systems running ntpd version 4.2.8p15 within the supported DDOS version include full leap second handling capabilities.
  • Data Integrity
    • Question: Can leap second adjustment cause issues with the Data Domain File System (DDFS), such as log consistency or snapshot scheduling?
    • Answer: The DD handle a leap second adjustment. DDFS can handle longer backwards time jumps than one second, and engineering has not seen any prior incidents where leap seconds caused an issue.
  • Precheck requirement
    • Question: Is it recommended to keep NTP enabled during a leap second event, or should a specific precheck procedure be followed?
    • Answer: It should be fine to leave NTP enabled during the leap second window. 

DDOS Codebase Validation

The following components confirm readiness for leap second handling:

Linux Kernel Validation - Verified

  • Kernel Version: Linux 5.4
  • Build: Linux 5.4.95 (as found in the kernel Makefile)

Leap Second Handling Capabilities:

  • Includes comprehensive leap second state management:
    • TIME_INS (insertion)
    • TIME_DEL (deletion)
    • TIME_OOP (out-of-phase)
    • TIME_WAIT (waiting state)
  • Integrated mechanisms for:
    • Leap second stress testing
    • Deadlock detection and prevention

DDFS Handling - Verified

  • The DDFS codebase includes recovery mechanisms for time adjustments, including backward time shifts.
  • Observed logic in the Virtual Tape Library (VTL) info cache:
    • Detects backward time movement
    • Automatically triggers database resynchronization:

      "time went backwards, resync database"

Operational Recommendation

  • The system can handle leap second adjustments without disruption.
  • NTP should remain enabled during the leap second window.
  • No additional mitigation steps are required.
 

 

Additional Information

Note: If running a newer NTPD version which is p17 (p17 vs p15 in BOM), it is even better for leap second support. 

Summary

Engineering validation confirms:

  • Linux 5.4 kernel includes required leap second fixes and safeguards
  • DDFS is resilient to backward time adjustments
  • NTP (ntpd 4.2.8p15 or later) fully supports leap second handling

 

Affected Products

Data Domain, Integrated Data Protection Appliance Family
Article Properties
Article Number: 000472018
Article Type: How To
Last Modified: 12 يونيو 2026
Version:  1
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