March 13, 2007 at 12:44 pm
I do not know if this is the correct place to post this, so feel free to move or delete this if it is in the wrong location. We just had a server's database backup fail due to lack of disk space. On investigating, it was discovered that the backup from Saturday had not been deleted by the Maintenance Plan. Further, the file had a create date/time of 3/10/07 at 9:00 PM. Our backup job runs at 8:00 PM. Checking the job logs showed that all the files created before 2 AM Sunday Mar 11 had the create time rolled forward by 1 hour. Please correct me, but I always thought that the DST change only rolled the system clock ahead, not all the file times. We don't think this will be a big problem for us, but I thought the rest of you might be interested in this.
March 14, 2007 at 6:08 am
From my experiences, this is a normal result of the DST change.
I haven't confirmed anywhere, but I suspect that Windows stores the File timestamp in GMT and when displaying it, converts to local time based on the current DST settings.
If you want to see this, take a test machine, create a sample file, check the timestamp, change the time zone to something other than your current time zone, then check the timestamp on the file. You should see the timestamp changed by the difference in time zone.
Now, if you look at a file on a server from machines that have different timezone settings, you could see different timestamp at the same time (I think)
I've had problems with SQL backup jobs not deleting the previous day's backup around DST change becasue the file is 23 hours old, which is less than "older than one day" specification on deleting old backups. It is usually a issue on one day per year, and then only if it causes a tape backup to go to a second tape.
March 14, 2007 at 7:42 am
This doesn't make sense to me. It seems to me that once a file is created, the create date\timestamp should be fixed, and not changed merely because the system time is changed at a later date.
March 14, 2007 at 8:44 am
It is not the time stamp that is changing. The file was created at 8pm EST and then the server received instructions to display all times in DST so it shows the file create date as 9pm DST which is the exact same moment in time. If you move back to EST it will show 8pm EST. In actual lapsed time that file was created 23 hours before your next back up so it was not 24 hours old.
March 15, 2007 at 6:47 am
To stop this being a problem, could you not set the maintenance plan to delete backups older than 22 hours instead of 24? This way it should always remain uneffected by daylight saving.
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