ADSM-L

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1996-04-09 17:20:50
From: "Pete Tanenhaus, ADSM Client Development" <pt AT VNET.IBM DOT COM>
Date: Tue, 9 Apr 1996 17:20:50 EDT
Date: 9 April 1996, 16:55:01 EDT
From: Pete Tanenhaus, ADSM Client Development        TANENHAU at GDLVM7
To:   ADSM-L at VM.MARIST.EDU
Subject: Daylight savings time for FAT on NT and Win95

I verified that this is a problem and a fix will be available
in the next PTF.

I did some research on this and it turns out that File dates and times
indeed are treated differently on FAT and NTFS. It appears that FAT
stores the local time and not the Universal Coordinated Time (UTC) as
NTFS does.

It also appears that different Win32 APIs dealing with date/time work
differently for FAT and NTFS.

The bottom line is that NTFS adjust for daylight savings and FAT does
not.

For example, if a FAT files was backed up last Friday at 4:30pm and restored
today, the filetime of restored file would be 5:30pm.

If the machine time is set back to last Saturday and the file is restored
the time would be 4:30pm.

The above example assumes that the machine is automatically adjusting for
daylight savings (control panel option).

NTFS files will always be restored with the same date with which they were
backed up.

This behavior explains why incremental backup is forcing all files backed up
in the non-daylight savings time period to be backed up again - the last write
time of the file stored on the server is exactly 1 hour less than that which
is reported by the local file system.

Anyway, I fixed the problem by using the DOS date and time for comparison/
restore purposes, which is always in local time.

If anybody is interested a detailed explanation of this behavior can be
found in the Microsoft Knowledge Base article number Q128126.


Pete Tanenhaus
ADSM Client Development
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