<font size=2 face="sans-serif">I think you found your answer: TSM
tracks files by pathname. </font><br><br><font size=2 face="sans-serif">So... if a file had path /w/x/y/z on
Monday. But was moved to /w/x/q/p on Tuesday, how would TSM "know"
it was the same file...?</font><br><font size=2 face="sans-serif">It wouldn't! To TSM it seems you've
deleted the first and created the second.</font><br><br><font size=2 face="sans-serif">Technically there are some other possibilities,
and some backup systems may use them, but NOT TSM:</font><br><br><font size=2 face="sans-serif">1) Record the inode number and generation
number and/or creation timestamp. Within a given Posix-ish file
system, that uniquely identifies the file.</font><br><br><font size=2 face="sans-serif">2) Record a strong (cryptographic quality)
checksum (hash) of the contents of the file. If two files have the
same checksum (hash) then the odds are</font><br><font size=2 face="sans-serif">we can use the same backup data for
both and don't have to make an extra copy in the backup system.
To make the odds really, really "long" you want to</font><br><font size=2 face="sans-serif">take into account the "birthday
paradox" and use lots and lots of bits. Long odds can also be
compared to the probability of losing a file due to a bug</font><br><font size=2 face="sans-serif">or an IO error or accident or disaster...</font><br><br><font size=2 face="sans-serif">For example SHA-256, might be strong
and long enough for you to believe in.</font><br><font size=2 face="sans-serif">Backup is not generally a cryptographic
game, so perhaps you should not worry much about some evil doer purposely
trying to confound your backup system.</font><br><font size=2 face="sans-serif">OTOH - if you have users who are adversaries,
all backing up into the same system... In theory one might "destroy"
another's backup.</font><br><br><font size=2 face="sans-serif">This save transmission and storage of
duplicates, but of course the backup system has to read the contents of
each suspected new file and compute the hash...<br></font><br><BR>