[kwlug-disc] Backup and Recovery in the 21st Century

unsolicited unsolicited at swiz.ca
Tue Jan 12 11:36:05 EST 2010


All true.

rsync is replication, not 'backup.'

BUT, (in addition) such replication gets your 'backup source' 
elsewhere where backups can take as long as they need to (up to the 
start of the next replication cycle), rather than dragging down the 
actual production server. (e.g. SQL / transaction logs.)

And rsync provides that 'within 24 hours' copy the file back 
accessibility, that another storage medium, even dump, doesn't have. 
([rsync] checksums too, if I remember correctly. Not that tar, etc., 
don't.)

Tiered effort.

Ultimately you want to get a copy off to removable media for safety 
(both access and physical) - which is how this thread started, with 
tape. Personally, I think tape is dead (usually), in favour of, say, 
multiple / swappable eSata enclosures.

One of the very nifty things about *nix is that the fact that it's 
tape is largely back end irrelevant. It's just some storage medium / 
destination - swap in something else, like eSata, and get on with your 
day.

Khalid Baheyeldin wrote, On 01/12/2010 11:09 AM:
> On Tue, Jan 12, 2010 at 9:46 AM, Adam Glauser <adamglauser at gmail.com 
> <mailto:adamglauser at gmail.com>> wrote:
> 
>     Khalid Baheyeldin wrote:
> 
>         The fact that it works on the file system level also has
>         advantages. You
>         can restore a partition EXACTLY to what it was before. This means
>         timestamps, ownerships, access times, ...etc.
> 
> 
>     Is the main advantage over using --archive with rsync that the
>     backup can reside on a filesystem that does not support all the
>     features of the source filesystem?
> 
> 
> Rsync as most people use it is not real backup. You have only one copy 
> on another machine (which is good), but you don't have versions. You 
> just have the latest sync point in there.
> 
> Rsync here is like RAID, it protects from one thing only (disk failure 
> in case of RAID, and machine failure in case of rsync). What they do not 
> protect against, is user error, e.g. someone deletes a file by mistake 
> then realizes it a week after, or an application bug corrupts data and 
> you realize that after 4 days.
> 
> With Rsync and RAID, you are out of luck. If you have real versioned 
> backup you can go back and retrieve your file from the older backup.
> 
> I have had a few instances of "oops!" and had to go to backup and found 
> what I deleted in it. Rsync and RAID do not provide that.
> 
> I am not saying that dump is the only such program. If you write a 
> script to do tar or cpio archives to another machine, then you have 
> versioned backups. But with dump you can do incremental and between the 
> full and (say) a 6 incremental, you can go back and get anything from 
> backup. If you leave a monthly or quarterly full then you are better too.
> 
> This is why I linked to the Tao of Backup because it explains what 
> backups should be. RAID and rsync do not do everything proper backup does.



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