[olug] To RAID or not to RAID

[Dan Linder]

This reminded me of an old script I wrote up to keep a number of copies of
the data but re-using the files on-disk if the data was the same.

Check out this URL: http://www.mikerubel.org/computers/rsync_snapshots/

But the gist of it is this (from the page):

rm -rf backup.3
mv backup.2 backup.3
mv backup.1 backup.2
cp -al backup.0 backup.1
rsync -a --delete source_directory/  backup.0/

If the above commands are run once every day, then backup.0, backup.1,
backup.2, and backup.3 will appear to each be a full backup of
source_directory/ as it appeared today, yesterday, two days ago, and three
days ago, respectively--complete, except that permissions and ownerships in
old snapshots will get their most recent values (thanks to J.W. Schultz for
pointing this out). In reality, the extra storage will be equal to the
current size of source_directory/ plus the total size of the changes over
the last three days--exactly the same space that a full plus daily
incremental backup with dump or tar would have taken.

BUT, BEFORE YOU IMPLEMENT THIS, PLEASE READ THE UPDATES ON THE URL LISTED
ABOVE.  THERE ARE SOME CLEANER METHODS TO DO THIS that will preserve the
ownership and permissions, and optimize disk usage after a number of backup
rotations.  (I'm sure someone has a better script that's up-to-date...)

I did experiment with using the Win32 version of rsync many years ago, but
I don't believe it supported the

Dan

On Mon, Sep 22, 2014 at 8:32 PM, Obi-Wan <obiwan at jedi.com> wrote:
>
> On 09/22/2014 06:19 PM, Lou Duchez wrote:
>>
>> Any chance you've got a friend out there on the Internets who would let
you keep a drive at his place?  For my remote backups, I do a two-step
process:
>>
>> 1)    rsync is a great way to back data up across a network (including
the Ethernet), especially where only a little data changes from one backup
session to the next.  So let's say I use rsync to back up my data to
"/backups/current" on the remote system.  Which I then follow with step 2
...
>>
>> 2)    /bin/cp -al /backups/current /backups/[date]
>>
>> What that does is create a dated backup directory, but thanks to the
magic of the "-l" flag, hard links (not symbolic links) to the files in
/backups/current are created.  That means I have a logical copy of
/backups/current that takes up almost no additional drive space because
it's pointing to the same files on the file system.  Now, if any of those
files in /backups/current is changed the next time I run rsync, the file in
/backups/current is unlinked first and a new file is created -- but the
link to the original in /backups/[date] is left completely untouched.
>
>
> I don't see anything in the rsync man page that indicates it will break
that hard link when updating an existing file.  How does your setup ensure
this will happen?  If the link isn't broken, then your old hardlinks will
get updated along with your current file when rsync changes it.
>
> --
> *Ben "Obi-Wan" Hollingsworth* obiwan at jedi.com <mailto:obiwan at jedi.com>
www.Jedi.com <http://www.jedi.com>
> The stuff of earth competes for the allegiance I owe only to the
> Giver of all good things, so if I stand, let me stand on the
> promise that You will pull me through. /-- Rich Mullins/
>
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