[CentOS] evaluating backup systems: rsync

Sun Jan 13 08:30:03 UTC 2013
Gordon Messmer <yinyang at eburg.com>

On 01/11/2013 01:37 PM, ken wrote:
>    From what I've read, rsync will work in the background and just fine
> while users (and several system processes) are copying, deleting,
> editing and other things which would confuse tar.

No, it doesn't.  rsync does not have any magic powder for making or 
keeping files consistent.  If you rsync a file that is actively being 
written to, the destination will probably be inconsistent (i.e. 
corrupt).  Don't use rsync, alone, for backing up any files that are 
open for writing.

If you want to make a backup that's consistent across a filesystem, you 
need to make a snapshot, mount it, and back up the snapshot content.  If 
there are files open for writing, you need to make them consistent while 
the snapshot is made.  While I rarely say nice things about Windows, 
this is an area where Linux falls far short.  There is no common 
mechanism for making files and databases consistent and making a 
snapshot for backups.  Admins must do this on their own.  If you aren't 
actively taking steps to make your backups consistent, they aren't.

> Plus, it handles the network stuff.

It doesn't really do that on its own, either.  Most people probably use 
rsync with ssh for a network link.  That's the default behavior if the 
source or destination is formatted properly.  It can be changed with the 
-e flag, or you can handle the pipe on your own.  rsync can run as a 
daemon, but I think that's most commonly used for publishing public data.