Two scripts to perform a backup of several block devices over network.

howto

The two backup scripts ``read.sh`` and ``write.sh`` will be executed as a pair,
to copy multiple devices or logical volumes from a host to a local computer.
To achive this, a number of steps must be taken:
1: Fill targets="" with the same sequence of targets for both scripts, the order being essential.
2: Make sure the targets to write to at the client/write.sh part are at least as large as the targets on the host/read.sh part.
3: We assume that the host runs an ssh server, but the client may not offer an ssh connection.
   To get data flowing over network from host to client we'll therefore build a reverse tunnel with ssh.
   ```ssh -R 62222:localhost:62222 $host -N```   
   Note that we use port ``62222`` on both sides, which is the same port as used with ``nc`` in both scripts.
4: Start ``write.sh`` before ``read.sh``, so that it already listens for incoming data before ``read.sh`` tries and failes to connect.

read.sh

#!/usr/bin/bash
# Be aware that dd has a leading /dev/!
sources=""
for s in $sources
do
        echo "Handling source: $s"
        dd bs=32k if=/dev/$s | gzip | nc -w 5 localhost 62222
        sleep 30
        echo "Done.."
done

write.sh

#!/usr/bin/bash
# Be aware that dd has a leading /dev/!
targets=""
for t in $targets
do
        echo "Handling data for $t" 
        nc -l -p62222 | gzip -d | dd bs=32k of=/dev/$t
        echo "Done.." 
done