Summary 


This article describes the importance of setting and maintaining the correct time on all computers in your DS-System's environment.


Details 
If the time on a computer that is running a DS-System (or DS-Billing, BLM, DS-Client, etc.) service / daemon must be changed:

  • Stop the service / daemon on the computer.
  • Stop the database instance (if any).
  • Change the time / date.
  • Restart the database instance and the service / daemon.


Consequences of changing the computer time on a source computer 
"Last modified time" of a file may cause problems. If you modify a file after changing the time, its time may be earlier than a version of that file that was already backed up.
Otherwise, the impact from a backup perspective is minimal.

Consequences of changing the computer time on a DS-Client 
Reports may show inconsistent data
Backup session may show inconsistent data since everything within reporting and generations are based on time.

However, the problems for the DS-Client can run much deeper because the current time on the DS-Client computer is automatically used during some processes:
Any restore where you select "latest generation of data" may restore an old backup (e.g. if you change the time back before the time of the actual backup session with the latest generation).
Retention may not have the required effect because it will count backwards from the changed time on the DS-Client (e.g. if your retention rules are based on keeping data for a number of days like "Keep all generations for the last 30 day(s)").
These are only a few potential problems. There are a lot of variable scenarios that will be unique to each customer's environment.

If you must change the time on a DS-Client, it may be better to stop backing up all the defined sets (suspend them), clone them and continue with new backups using the cloned sets. This is probably not something that customers will want, however it is the only way you can ensure that future operations have the required effect.

NOTE: These problems are most likely to occur if the time on the DS-Client computer is changed backwards. Problems will occur if the next backup session runs at a time that is before the time of the most recent backup session.

Consequences of changing the computer time on a DS-System / DS-Billing server 
NOTE: For a production DS-System, there should be no instance when you need to change the date / time. It must be correct from the beginning (as of the moment it receives the first DS-Client's data), in order to preserve the integrity of the logs.

Reports may show inconsistent data. This is a serious problem for Invoice reports.


Daylight savings time 
Daylight savings is transparent as long as the computer is configured to switch automatically ("Automatically adjust clock for daylight savings changes").
When the clock moves forward an hour:
oA one hour gap appears in logs (e.g. Activity Log), usually from 02:00-03:00.
When the clock moves backward an hour:
oAll activities in the two hours appear in the single hour (usually 01:00-02:00) in logs.


NOTE: The starting time of some scheduled processes (like Daily Admin) may show the hour difference until the computer is restarted.