[CentOS] evaluating backup systems: rsync

Fri Jan 11 22:05:35 UTC 2013
m.roth at 5-cent.us <m.roth at 5-cent.us>

ken wrote:
> On 01/11/2013 02:33 PM m.roth at 5-cent.us wrote:
>> ken wrote:
>>> On 01/11/2013 12:36 PM Les Mikesell wrote:
>>>> On Fri, Jan 11, 2013 at 11:29 AM, ken<gebser at mousecar.com>   wrote:
>>>>> Considering using rsync on a couple systems for backup, I was
>>>>> wondering if it's possible, and if so how difficult is it, to delete
>>>>> files which have been backed up (in order to save space on the backup
>>>>> media).
>>>>> Anyone with experience doing this?
>> We use rsync here. Actually, we've got a home-rolled system. We created
>> timestamped backups, which also removes them after a configuration file
>> item of how many days or weeks. Note that we *heavily* use rsync's parm
>> to use hard links, which saves a lot of space.
> Cool.  Thanks for mentioning time-stamps.  I've been assuming that rsync
> would maintain the source files' original permissions and timestamps.

It does, if you use the right parm (parameter). We timestamp the backup
directories that we create, like spiderman.2013-01-11-17:01

> (Heck, even tar from decades past would do that.)  I hope that wasn't an
> unwarranted assumption.  It's good to hear too that I can configure how
> long to keep files on destination which have been deleted from the
> source (if that's what you meant).
> Mark, maybe you could explain what a "parm" is and how using hard links
> saves space.

A hard link isn't easy: it's an inode that is referenced by more than one
other inode. In effect, it's a pointer, rather than a reference, so that
it really, in effect, acts like the real file, and is almost
undistinguishable from one. You don't actually delete the real file until
all hard links pointing to it are gone.

Google it a bit - it really is hard to wrap your head around.

A symlink is like a reference "this file is found over there", where a
hard link is like "I point to that location, the same way the inode that
was created when the file was points to the location.

I know that's not right. As I said, try googling.