Re: One way SSH connection and incremental/differential backup

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On 25/10/2019 00:45, Kamil Renczewski wrote:
> Hello,

Hello,

> My current (rsync) based backup mechanism uses one-way SSH
> connection. I Wonder if could make a switch to DAR and preserve the
> one-way SSH connection restriction.

first I'm not sure to understand what you mean by "one-way SSH
connection" as ssh is always bidirectional (order/command in one way,
output/result on the other way).

I assume you mean that there is not ssh server on the storage host, so
all ssh session must be launched from the honey (storage server) to
flower (the host to backup).

> 
> I've read dar_ad_ssh 
> (http://dar.linux.free.fr/doc/usage_notes.html#netcat_ssh), this 
> explains how to make a differential backup when connection from 
> backup/flower host to a storage/honey host is possible. My case is
> a little different. My host that need to be backed up have no idea
> of the storage/honey host.
> 
> The problematic step for me is to execute (on the backup/flower
> host):
> 
> ssh honey dar_slave backup > todar < toslave &

dar_slave has to run on the host where is located the archive of
reference (honey), and has to be connected to dar by two pipes.

*** first option:
using pipes with ssh means using stdout and stdin of the command that
is ran remotely. You could use these pipes for dar to exchange with
dar_slave, but then you will have not pipe left for the resulting
backup, which will have to be saved locally on flower.

on honey:
 mkfifo todar toslave

 dar_slave -i toslave -o todar backup &
 ssh flower dar -c diff_linux -A - -S 10M -S 5M -p < todar > toslave
 scp flower:diff_linux.*.dar . && ssh flower rm diff_linux.*.dar


here diff_linux is written where dar is run, thus on flower and this
backup can be copied/moved to honey afterward. The ssh session carries
the exchanges between dar_slave and dar, no more the generated archive
as stated in the documentation you referred.

*** second option:
  create an isolated catalogue of the archive of reference upload it
to flower and use dar over ssh from honey referring this isolated
catalogue

on honey:
   dar -C cat_backup -A backup -z
   scp cat_backup.1.dar flower:/tmp

   ssh flower dar -c - -A /tmp/cat_backup | dar_xform -s 10M -S 5M -p
- - diff_linux
   ssh flower rm /tmp/cat_backup.1.dar


> 
> I am wondering if there is a way that I could modify this step so
> it can be done only from storage/honey host.

I would try option 2 which is simpler and probably more adapted to
your need as you seem having a storage host that holds all the backups

> 
> Kamil Renczewski
> 

Regards,
Denis


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