Matching

[EricBergan]

The blurb about 6.0 says:

 

 

 

Save Precious Media Space Hard drives hold a lot of data. To optimize backups, Retrospect recognizes identical files on one or more computers and backs up just one copy.

 

 

 

So if I install a software package (say MS Office) on multiple client machines, the files will only be stored once in a backup set? If that is correct, is this new in 6.0?

 

 

 

Thanks.

 

 

 

Eric

[AmyJ]

Yes, if you have exact, unchanging files that exist across multiple computers, as in the case of a software installation, Retrospect will only back them up once. This is not new to 6.0 - Retrospect has always used this matching scheme.

 

 

 

Matching is the scheme for comparing file attributes to determine whether files are identical, which then allows intelligent copying to avoid redundancy. Also see incremental backup.

 

 

 

Retrospect uses several matching criteria to find new or changed files. If one of the criteria has been changed, Retrospect will back up the file again. On Windows, Retrospect looks at creation date and time, modified date and time, size and name. If match only in same location option is set, Retrospect matches on the path, volume name and drive letter also.

 

 

 

By default, the archive attribute is not used as a matching criteria in Windows, allowing for true and reliable backups to multiple backup sets.

 

 

[EricBergan]

That's interesting, since I also email'ed tech support about this, and the reply was that no, it doesn't do matching across client computers.

 

 

 

That certainly seems to jive with my experience that if I upgrade Office or install a new application on a few machines, each of those machines seems to have a larger backup next time, reflecting the new files.

 

 

 

Eric

 

 

[AmyJ]

If any of the file criteria are different between client machines (creation date and time, modified date and time, size and name) the file(s) will get backed up from each machine. Retrospect must look at all criterion to determine whether or not the file is _exactly_ the same file.

[EricBergan]

Very interesting, learn something new every day!

 

 

 

I dug around, and can see the difference by comparing the snapshot with the session for a new backup set of a few clients, after letting the clients do "full" backups.

 

 

 

There doesn't see to be any easy way (report, mention in log file, etc) of measuring what is going on here, is there? It would make it easier to plan backup space usage, particularly when doing upgrades of software.

 

 

 

Anyway, thanks for helping me through this!

[pls]

So if I have, say, Office installed on 5 machines on a net, Retrospect won't recognize the files as duplicates unless they 5 copies were installed at EXACTLY the same time?

 

 

 

Seems to make the cross-machine matching rather useless. Or did I misunderstand.

 

 

 

++PLS

[AmyJ]

The matching criteria (creation date and time, modified date and time, size and name) is file specific, not location specific. An office file installed from a CD should be identical across machines, unless changes are actually made to the files during installtion. For example, some of my Office files have creation and modification dates of February, 2001 - despite a clean installation of Office earlier this year. Many programs have certain files that are modified on installation - these files will not match against installations on other computers.