Mac Forum / Programming / Perl / July 2005

Dear Perlers,
    A little while ago I asked about solutions to the graceless  
failure I was experiencing with psync (would look like it copied  
data, but would happily create zero-byte files once out of room,  
without complaining;  and on re-psync, would copy reams of links,  
making me unsure that everything'd been copied before, since it was  
copying again ...).
    Rsync was mentioned as a solution, and using rsync under Tiger  
or using rsyncX, whis looks plausible.  However, when I've tried this  
I've gotten errors.  Also, others complain it's not ready for prime  
time: <http://www.macdevcenter.com/pub/a/mac/2005/07/22/backup.html?
page=2> (see comments in bottom;  these reflect my experience, with  
broken pipe errors, etc.)
    One happy note was that rsync has a flag for comparing checksums  
during rsync runs.  This assures that copies really put the right  
data -- and all the right data -- in each of the files.  The downside  
is that I have no idea what it does to compaare checksums on extended  
attributes, resource forks, or the like.  The psync script could  
certainly have md5 sums added to the "scanning" cycle of both source  
and destination, and have a scan of all copied items to ensure the  
sums were correct ... but I don't have an instinct for the least-
overhead way to do this.  Also, doing checksums over a connection to  
a remote volume would create ridiculous traffic:  the machine running  
psync would need to receive all the data in all the files to do a  
checksum on each, which is in my view why rsync has a client/server  
model (to do processing on each end, reducing transmission of data).
    So my questions are:
    (1) Does psync really have an issue with symlinks, and recopy  
symlinks all the time? (or is there a difference between relative and  
absolute paths in symlinks, and does psync treat them differently and  
thus fail to recognize a good copy during pre-copy checks, forcing  
recopies?)
    (2) Does anyone have a solution for copy verification under  
psync, or should I experiment rolling my own "verify" flag in the  
psync script?
    (3) Does anyone have experience getting backups to work well  
under rsync, with or without perl involvement?
    Thanks in advance :-)
    Best regards,
    Chris