Effect on Daylight Savings on attributes of backup files


B

Bob S

I use a portable drive to keep files synchronized between my
home and office computers.

The problem is that when Daylight Savings Time arrives the
files on the portable drive get out of sync with the desktop
computers by one hour. This doesn't necessarily cause a
problem with my synchronization program, because the time
difference apparently doesn't change the files' CRC numbers
(if that's what they're called). I wouldn't have expected
that, but it apparently seems to be so.

Still, once Daylight Savings Time strikes, in the file
attributes the creation and modification dates of *all* of
the files on the portable drive become one hour "older" than
the ones on the desktops. In the fall, when Standard Time
comes back, the converse happens.

Because there are so many files (well over 100,000), were I
to synchronize them by time of modification rather than by
CRC, it would take forever to get them back in sync. Also,
I'm concerned that some day this "de-synchronizing" of the
file times could cause confusion leading to a mistake on my
part if the time of creation or modification of a file ever
became important for some reason.

I'd appreciate any suggestions on how to keep the times
coordinated on these files. Leaving the portable drive
connected to a desktop overnight doesn't do it.

Thanks.
 
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L

LD55ZRA

You should switch off your computer for one hour between 1:00:00 and 2:00:00
or between 2:00:00 and 1:00:00 depending on whether the clocks are going
forward or backward. The system is smart enough to deal with these things.

In actual fact the switching off is only required for one minute before the
hour and one minute after the hour. So two minutes in total. I would have
thought most people's systems are logged off during this critical time on
our planet! Or clocks (In United Kingdom) don't go forward until 28th March
2010. Normally last Sunday in March.

hth
 
B

Big_Al

LD55ZRA said this on 3/14/2010 4:02 PM:
You should switch off your computer for one hour between 1:00:00 and 2:00:00
or between 2:00:00 and 1:00:00 depending on whether the clocks are going
forward or backward. The system is smart enough to deal with these things.

In actual fact the switching off is only required for one minute before the
hour and one minute after the hour. So two minutes in total. I would have
thought most people's systems are logged off during this critical time on
our planet! Or clocks (In United Kingdom) don't go forward until 28th March
2010. Normally last Sunday in March.

hth

Bob S said:
I use a portable drive to keep files synchronized between my
home and office computers.

The problem is that when Daylight Savings Time arrives the
files on the portable drive get out of sync with the desktop
computers by one hour. This doesn't necessarily cause a
problem with my synchronization program, because the time
difference apparently doesn't change the files' CRC numbers
(if that's what they're called). I wouldn't have expected
that, but it apparently seems to be so.

Still, once Daylight Savings Time strikes, in the file
attributes the creation and modification dates of *all* of
the files on the portable drive become one hour "older" than
the ones on the desktops. In the fall, when Standard Time
comes back, the converse happens.

Because there are so many files (well over 100,000), were I
to synchronize them by time of modification rather than by
CRC, it would take forever to get them back in sync. Also,
I'm concerned that some day this "de-synchronizing" of the
file times could cause confusion leading to a mistake on my
part if the time of creation or modification of a file ever
became important for some reason.

I'd appreciate any suggestions on how to keep the times
coordinated on these files. Leaving the portable drive
connected to a desktop overnight doesn't do it.

Thanks.
My PC was in hibernate all night and this happened to me too today.
Wouldn't your logic apply there or should you do a real power down?

Granted my list of files is smaller and I have the backup never to copy
"older" files, so some updated from before last time change were still
there and thus the same hour, it only updated the recent changes in 6mos
or so. I suspect for me that will never happen again now that I've
done the update 2 times in a row now with "older" skipped.
 
J

John Wunderlich

I use a portable drive to keep files synchronized between my
home and office computers.

The problem is that when Daylight Savings Time arrives the
files on the portable drive get out of sync with the desktop
computers by one hour. This doesn't necessarily cause a
problem with my synchronization program, because the time
difference apparently doesn't change the files' CRC numbers
(if that's what they're called). I wouldn't have expected
that, but it apparently seems to be so.

Still, once Daylight Savings Time strikes, in the file
attributes the creation and modification dates of *all* of
the files on the portable drive become one hour "older" than
the ones on the desktops. In the fall, when Standard Time
comes back, the converse happens.

Because there are so many files (well over 100,000), were I
to synchronize them by time of modification rather than by
CRC, it would take forever to get them back in sync. Also,
I'm concerned that some day this "de-synchronizing" of the
file times could cause confusion leading to a mistake on my
part if the time of creation or modification of a file ever
became important for some reason.

I'd appreciate any suggestions on how to keep the times
coordinated on these files. Leaving the portable drive
connected to a desktop overnight doesn't do it.

This pops up every year about this time.

This is caused by the disk file systems involved. NTFS file systems
(typically used by Windows XP and newer) save file date/time as an
absolute time in UTC (GMT) format. FAT and FAT32 file systems
(likely to be what your external drive is) stores dates/times in
"local time". This can cause a 1 hour discrepancy when Daylight
Savings time comes into/out of effect or when moving a computer
between time zones.

To correct this permanently, format your external drive as NTFS
(backup your data first).

HTH,
John
 
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B

Bob S

LD55ZRA said:
You should switch off your computer for one hour between 1:00:00 and 2:00:00
or between 2:00:00 and 1:00:00 depending on whether the clocks are going
forward or backward. The system is smart enough to deal with these things.

In actual fact the switching off is only required for one minute before the
hour and one minute after the hour. So two minutes in total. I would have
thought most people's systems are logged off during this critical time on
our planet! Or clocks (In United Kingdom) don't go forward until 28th March
2010. Normally last Sunday in March.

My memory may be a bit feeble, but I have the impression
that in the past I've had the computer shut down when the
time change occurred, but I still had the problem with files
being out of sync. Not sure though. In any case, I'll follow
John's advice about formatting the drive as NTFS.

Thanks for the response.
 
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