On Fri, Mar 10, 2006 at 01:39:24PM -0600, Les Mikesell wrote: > Rsync incrementals turn on the option to skip files where the length > and timestamp match, making them considerably faster but more likely > to accidentally miss a changed file. However, since they always work > against the last full, you end up re-copying things that were copied > in previous incrementals. There is some room for improvement here.
A while back, I tried using Retrospect backup's linux client for backup. Aside from quickly discovering that they weren't prepared to deal with some of the long pathnames and filenames on my machine, I discovered a much more fundamental problem. By default, retrospect tries to do something similar to backuppc, in that files from previous backups aren't copied again, but just refer to the old file. Essentially, it is kind of like backuppc, with rsync timestamps and always doing full backups (retrospect doesn't expire old data, you have to start a new 'full' backup to do that). However, I discovered they were just using file timestamp and size to indicate duplicates. That meant that any file of the same size and timestamp would be considered the same (no hash). It completely mangled the gentoo portage tree, since it gets rsync updated, and has many files that just consist of a few MD5 hashes. Large groups of these files are the same size, and are updated within a second. Very bad assumption for them to make. What is much better is to only consder the timestamp for the same given file (like rsync is doing). This at least prevents merging arbitrary files. Also, as far as I know, every backup program that does incrementals looks at just the timestamp field. On unix, the ctime and mtime field together will always tell you of a file change, as long as the system clock is monotonically increasing. On windows, all bets are off, and I'm not sure there really is anything to do but read the file in and hash it's entire contents. Dave ------------------------------------------------------- This SF.Net email is sponsored by xPML, a groundbreaking scripting language that extends applications into web and mobile media. Attend the live webcast and join the prime developer group breaking into this new coding territory! http://sel.as-us.falkag.net/sel?cmd=lnk&kid=110944&bid=241720&dat=121642 _______________________________________________ BackupPC-users mailing list BackupPC-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/backuppc-users http://backuppc.sourceforge.net/
