[SATLUG] downsides to rsyncing entire file system?

[Travis Miller]

Let me start by saying, I do this also and it does work pretty well.  BUT, there 
are some issues to consider when rysncing systems.   You have to realize that 
the backup you are getting when using rsync is not a single "snapshot" of the 
file system - its more of a "photo album" of snapshots.  Maybe I should try to 
explain a little more.

To get a really consistent backup you need to be able to capture, in an instant, 
the entire file system and make a copy of it.  Unfortunately due to file system 
size this is impossible with rsync.  This is possible, I believe, using LVM or 
XFS.  Lets say you are making a backup of a webserver, and on this webserver you 
are also running MySQL.  Your backup starts at 3:00am but is just so happens 
that some user decides to login and make some changes to their files at the 
exact same time - a time line of events follows:

03:00:00 - backups starts and begins backup of entire system
03:00:01 - user login
03:00:02 - user uploads new PHP script to use new database format
03:00:03 - rsync updates home directories
03:00:05 - rysnc completes changes and exits
03:00:07 - user updates mysql database with new tables.

04:00:00 - server crashes
04:10:00 - server back up and running from backup server
10:30:00 - user calls because his PHP/MySQL has been failing all morning, he did 
not realize it and has just lost $20K in sales.

Of course there are better ways of replicating mysql, but my point stands.  When 
you simply use rsync to make backups you are getting copies of individual files 
as rsync gets to them - not copies of entire file systems.

Just something to think about!

- Travis




Jeremy Mann wrote:

> Nope, we do it on several servers here and across the US. The only
> thing that could possibly be a downside is the first time you run it,
> it will take longer the first time. But once that's done, add
> --no-whole-file to your rsync script and you'll just transfer the
> changes instead of the whole file.
> 
> 
> 
> On Thu, 9 Sep 2004 12:15:52 -0500 (CDT), eli at then7.com <eli at then7.com> wrote:
> 
>>just like the subject says, are there any downsides/pitfalls to rsyncing
>>the whole file system from a live server to a backup server?
>>
>>~e
>>
>>_______________________________________________
>>Satlug mailing list
>>Satlug at satlug.org
>>http://alamo.satlug.org/mailman/listinfo/satlug
>>
> 
> 
> 
>