Dean,

Here's the procedure Retrospect goes through when deciding whether to copy
files:

Scan drive
Compare files scanned with backup set.
Mark files that have changed/are new.
Copy files...

Note I said "compare...with backup set." Retrospect does a file-by-file
compare, meaning it compares the FILES on your drive to the FILES on your
backup set. No matter what drive or computer they were originally backed up
on.

That said, it's doubtful your 30 System Folders are exactly identical. To
test this, try a backup of a System Folder to a new or recycled backup set.
Now, start an immediate backup, matching enabled, of another System Folder.
Don't start the backup but click Preview. (Alternatively, you may be able to
browse a System Folder in Configure>Volumes, select all, browse another
System Folder, and paste.) All checked files without diamonds next to them
are different and will be copied. You can get info/properties on any file in
a Browser, so if there are specific files you think Retrospect should not
want to copy, take a closer look...

Matthew Tevenan
Technical Support Specialist
Dantz Development Corporation
925.253.3050 
[EMAIL PROTECTED]

> From: Dean Brissinger <[EMAIL PROTECTED]>
> Reply-To: "retro-talk" <[EMAIL PROTECTED]>
> Date: Thu, 29 Jun 2000 10:32:22 -0600
> To: "retro-talk" <[EMAIL PROTECTED]>
> Subject: Re: Storage space smarts
> 
> On a side note, does Retrospect check for identical files
> between backup clients?  I have 30 macs with identical system
> folders.  I really only need to backup those system files once.  If
> retrospect was so smart, I could do full backups site wide and get
> most efficient coverage with minimal tape space.  I note it tends to
> backup more than it needs to because of volume name, time stamp, etc.
> 
> 
> At 3:49 AM -0700 06/29/00, Ming-Li wrote:
>> Hi Matthew,
>> 
>>> Retrospect uses several matching criteria to compare files
>>> that have already been backed up to what is about to be backed
>>> up. If one of the following has been changed at all,
>>> Retrospect will back up the file again:
>>> 
>>> MAC files:
>>> name, size, type, creator, creation date and time,
>>> modify date and time, and label.
>>> 
>>> PC files:
>>> name, size, modify date and time, file system.
>> 
>> Have you ever consider using something even more accurate as the
>> criterion--say, CRC32, or some sort of file signature? Will it
>> slow down Retrospect significantly than the current approach?
>> 
>> I'm asking because I've found many different applications put
>> same version of system files (dll and such) with different
>> date/time. The file name, size and version no. (by checking the
>> file's properties) stay the same, and a binary comparison would
>> show the two files are identical. They have touched the
>> date/time probably because they want all their files to have the
>> same date/time, or because the original software development
>> package (MS C++, Delphi, etc.) did so. And some other software
>> would make the date/time of its installation the date/time of
>> all the files it put in, regardless their original date/time.
>> 
>> Under current design, Retrospect would back those files up
>> again.  By way of CRC32 check, Retrospect would find those files
>> are indeed identical to the original ones and skip them.  It
>> would not only save storage space, but also give me extra
>> confidence for whenever I catch some new application overwriting
>> my system files, I can look in Retrospect's backup preview
>> window and find which of them are in fact identical (hence no
>> worry) and which are different (so I might have to restore my
>> backed up version to see which one is in fact newer).
>> 
>> I don't know if any application would change a file's content
>> without changing its date/time and size.  But if that happens, a
>> CRC32 check would expose them, too.
>> 
>> --
>> Best regards,
>> Ming-Li
>> 
>> 
>> 
>> 
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> 
> 
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