[rear-users] Article about ReaR in German Linux Magazin

Schlomo Schapiro schlomo at schapiro.org
Sat Mar 12 20:08:04 CET 2016


​Hi Oli,​

On 11 March 2016 at 17:40, Oliver Hoffmann <oliver at g.dom.de> wrote:

> something I need to get straight about mkrescue. If I just do a rear
> format and mkrescue creating a USB stick and boot it up then I would be
> dropped to the rescue shell.
>

​I would call it "boot the rescue system", but yes.
​


> If I just do a rear rescue then the result would be a naked system as it
> was before but without any data or even extra binaries, won't it?
>

You still have to run rear recover to see any action. ​Probably doing that
exactly as you wrote will actually wipe your system, reformat the disks and
prompt you to restore the files into /mnt/local.

​


> Means this is only useful if I try to repair the system rather than
> carry out a rescue.
>

​Yes, you could use the rescue system to repair a system. However, that is
not the main purpose.


> In other words in most of the cases mkbackup is what one wants, isn't it?
>

​That depends on the value of the BACKUP variable in your config (see rear
dump​).

If you use one of the internal backup methods like BACKUP=NETFS then you
are correct and users should use rear mkbackup. The difference between rear
mkrescue and rear mkbackup is that rear mkrescue will only create the
rescue image while rear mkbackup will both create the rescue image and also
create a new backup.

​If you use an external backup method, e.g. BACKUP=TSM, then rear mkbackup
and rear mkrescue​ do exactly the same: Create a new rescue image. In this
mode the assumption is that your external backup system already has a full
(or relevant) backup of your system. Running rear recover in the rescue
system will then wipe the system, recreate the partitions and file systems
and instrument your external backup software (e.g. TSM) to actually restore
the files.

To understand this distinction you need to see the original purpose for
which we created ReaR: Doing bare metal disaster recovery with backup
software that does not support this. Or where the bare metal addon is very
expensive.

I wrote rear 1.0 in 10 days for a client who had Galaxy as his backup
software. The bare metal addon of that backup software was sold at about
1000€ per server. With the amount of servers that the client wanted to
cover (about 50), contracting me to write rear was actually much cheaper
for them :-) And rear worked much better than the proprietary bare metal
solution because it supported all custom drivers and worked fully automated.

HTH,
Schlomo
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