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Coupling Facility - TIMEZ Command during Daylight Saving Time Changes

Document Author:
Additional Author(s):

Gregory Hutchison
Noshir Dhondy

Document ID:


Doc. Organization:

Washington Systems Center

Document Revised:


Product(s) covered:

# 2064; # 2066; # 2084; # 2086; # 2094; # 9037-002; IBM eServer zSeries; IBM System z; Sysplex Timer; S/390; z9-109; zSeries 800; zSeries 890; zSeries 900; zSeries 990; zSeries

Abstract: This tip gives advice on handling Daylight Saving Time (DST) changes in a Coupling Facility when connected to a Sysplex Timer or when using Server Time Protocol (STP).

The sysplex timer and STP requires 3 offset values:
  1. Leap Seconds
  2. Time Zone Offset
  3. Daylight Saving time offset

The sysplex timer and/or STP transmits 2 offsets to the attached servers:
  1. Leap Seconds
  2. Local Time Zone = Time zone + Daylight Saving time offset

With a CF system connected to a Sysplex timer or using STP, the following will occur:

During POR and LPAR initialization LPAR will set the TOD to the ETR time or Coordinated Server Time (UTC + Leap Second Offset) value from the sysplex timer or STP.
(Reference Doc # SG24-2070 for more details regarding Time Management and Sysplex Timer found at )
(Reference Doc # SG24-7280 and SG24-7281 for more details regarding Server Time Protocol found at )

When the CF image partition is activated the CF code only uses the ETR time or CST from LPAR, PLUS either the image profile 'User Specified Time Offset' OR the 'TIMEZ' offset. The 'TIMEZ' offset will override the 'User Specified Time Offset'. CF code does not use the Local Time Zone offset.
This is why you are not seeing the change when you do the DI TIMEZ.
If you issue a change to the TIMEZ for a 4w offset then the policy will be set so the CF time will match the sysplex timer or the STP panels.

In the future when Daylight Savings Time needs to be adjusted, it is recommended that you use the TIMEZ command with the appropriate value. This will avoid the need to do a reactivate of the CF partition.

Here are some commands helpful for timezone that can be issued from oprmsg:
help timez help information on how to set timezone
di timez displays current timezone setting
timez 4 west (Example: set timezone to EDT when Daylight Savings time is in effect)
timez 5 west (Example: set timezone to EST when Daylight Savings is not in effect)




Operational Management


IBM System z Family



Coupling Sysplex Daylight Saving Time DST

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