From c32707148292d104c66276b43796d6057c8c7a5d Mon Sep 17 00:00:00 2001 From: Daniel Wilhelm Date: Fri, 18 Apr 2014 17:08:42 +0200 Subject: 3.10 --- BUILD/Help/html/advanced/DaylightSavingTime.html | 71 ++++++++++++------------ 1 file changed, 34 insertions(+), 37 deletions(-) (limited to 'BUILD/Help/html/advanced/DaylightSavingTime.html') diff --git a/BUILD/Help/html/advanced/DaylightSavingTime.html b/BUILD/Help/html/advanced/DaylightSavingTime.html index 4fffe036..b29a612a 100644 --- a/BUILD/Help/html/advanced/DaylightSavingTime.html +++ b/BUILD/Help/html/advanced/DaylightSavingTime.html @@ -3,9 +3,9 @@ - + - + @@ -17,53 +17,50 @@ H2 { margin-bottom: 0.21cm } H2.western { font-family: "Arial", sans-serif; font-size: 14pt; font-style: italic } H2.cjk { font-family: "MS Mincho"; font-size: 14pt; font-style: italic } - H2.ctl { font-size: 14pt; font-style: italic } + H2.ctl { font-family: "Mangal"; font-size: 14pt; font-style: italic } A:link { so-language: zxx } --> - +

Daylight -saving time

+saving time (Windows)

A +common problem synchronization software has to deal with are +-1 hour +file time shifts after a Daylight Saving Time (DST) switch has +occurred. This can be observed for example when a FAT-formatted +volume is compared against an NTFS volume as frequently happening +with USB memory sticks. Files that previously appeared to be in sync +are now shown with an one hour modification time offset, although +they have not been modified by the user or by other means.

The -Windows operating system exhibits quite a unique behavior when -handling timestamps on NTFS file systems. This leads to a well-known -issue that all file synchronization software has to handle:

During -daylight saving time switching, (local) file times are shifted by one -hour on NTFS file systems, while NO shift occurs on FAT/FAT32 drives -(as used by most USB sticks)! Thus when synchronizing an NTFS against -a FAT32 volume file times become asynchronous twice a year!

+reason for this strange behavior lies in the way NTFS and FAT drives +store file times: NTFS stores time in UTC format, while FAT uses +local time.

When +times stored in these two different formats are compared, one format +has to be converted into the other first. In both cases Windows uses +the current DST status as well as current time zone information for +its calculations. Consequently the result of this comparison is +dependent from current system settings and in particular file times +that used to be the same can show up as different after a DST switch.

For a -comprehensive discussion about this issue refer -to:
http://www.codeproject.com/KB/datetime/dstbugs.aspx

+detailed discussion about this issue refer to: +http://www.codeproject.com/KB/datetime/dstbugs.aspx

Solution:

In -order to avoid re-copying files that have a modification time -difference of +-1h FreeFileSync offers a global option: Menu -> -Advanced -> Global settings: Ignore 1-hour file time difference.

If -"Ignore 1-hour file time difference" is checked, all -files with a +-1h difference are treated as having the same time. -This also handles different file time precisions (NTFS: 100ns, -FAT/FAT32: 2 seconds) by allowing a 2 second tolerance .

Files -that have a deviation of less than one hour are categorized as -conflicts. The reasoning is that these files surely have been -modified on at least one side since last synchronization. But during -one of the two daylight saving time switches per year the older file -is shown pretending a newer date which can lead to data loss (when -using the rule to overwrite older with newer files).

- Note:
If synchronization - takes place between NTFS ↔ NTFS or FAT32 ↔ FAT32 this - checkbox provides no advantage and can be left unchecked.

-

+

Luckily +FreeFileSync users need not to worry about this issue. Each file on a +FAT volume automatically gets additional meta data encoded in its +creation date that enables a correct file time calculation. This not +only solves all DST issues but also time shifts that occur due to +travel between different time zones.

\ No newline at end of file -- cgit