Skip to main content

Differential Backups Made Simple

To backup or not to backup.  That is the question.

Who likes to make backups? Anyone, Anyone?

Hmm, I thought so...

Versioned Backups
I prefer to make backups with very simple tools, since when things go south, I don't want to have to install a complicated system just to get my data back.

Most UNIX backup systems are based on rsync and by using a careful system of  hard links (multiple new names for the same old file), differential backups can save you oodles of disk space in the long run, while making it very easy to step through an archive and retrieve specific versions of old files:

Three for the Price of One
The original article by Mike Rubel describes how to keep three backups for the price of one, using a combination of hard links and rsync. That idea then spawned the rsnapshot (pull) and rdiff-backup (push) scripts.

The method described below, creates three directory trees of all my data for today, some day and who knows when, without using significantly more disk space than a single backup.  One could similarly expand it to five, ten or more backups - it only depends on your use case and forgetfulness. I can browse the tree on the backup server using a common file browser and click-drag-drop a lost/damaged file back to the host.  This is as simple as it gets and just the way I like it.

Since the PSU of my Raspberry Pi server blew up, I now have a little NUC with a 2TB solid state disk that has all my music, movies and backups as a WiFi enabled file server, using this idea to good effect.   (The RPi is fine, it just needs a new USB widget.)

Differential Backup Script
On my MacBook, my backup script is directly based on Mike's and looks like this:
#! /bin/bash
# Rsync to Muzak and keep 3 old hard linked copies.
# Assumes the public key is installed in /home/herman/.ssh
ssh herman@muzak "mv ~/Backups/Herman.3 ~/Backups/Herman.tmp"
ssh herman@muzak "mv ~/Backups/Herman.2 ~/Backups/Herman.3"
ssh herman@muzak "mv ~/Backups/Herman.1 ~/Backups/Herman.2"
ssh herman@muzak "mv ~/Backups/Herman.0 ~/Backups/Herman.1"
ssh herman@muzak "mv ~/Backups/Herman.tmp ~/Backups/Herman.0"
ssh herman@muzak "cp -al ~/Backups/Herman.1/. ~/Backups/Herman.0"
rsync -avze ssh --progress --delete --max-size=20M --exclude "*Trash*" --exclude "*bak" \
--exclude "*old" --exclude "*cache*" --exclude "*Cache*" --exclude "*iso" ~/ herman@muzak:~/Backups/Herman.0/

The script follows the principle of: Include everything and Exclude the cruft. This makes the script maintenance free.

I simply run this little script whenever I feel like it.

La voila!



Popular posts from this blog

Parasitic Quadrifilar Helical Antenna

This article was reprinted in OSCAR News, March 2018: If you want to receive Satellite Weather Pictures , then you need a decent antenna, otherwise you will receive more noise than picture. For polar orbit satellites, one needs an antenna with a mushroom shaped radiation pattern .  It needs to have strong gain towards the horizon where the satellites are distant, less gain upwards where they are close and as little as possible downwards, which would be wasted and a source of noise.  Most satellites are spin stabilized and therefore the antenna also needs circular polarization, otherwise the received signal will flutter as the antennas rotate through nulls. The helical antenna, first proposed by Kraus in 1948, is the natural solution to circular polarized satellite communications.  It is a simple twisted wire - there seems to be nothing to it.  Various papers have been published on helix antennas, so the operation is pretty well understood. Therefore,

Patch Antenna Design with NEC2

The older free Numerical Electromagnetic Code version 2 (NEC2) from Lawrence Livermore Lab assumes an air dielectric.  This makes it hard (but not impossible) for a radio amateur to experiment with Printed Circuit Board Patch antennas and micro strip lines. Air Spaced Patch Antenna Radiation Pattern You could use the free ASAP simulation program , which handles thin dielectrics, you could shell out a few hundred Dollars for a copy of NEC4 , You could buy GEMACS if you live in the USA, or you could add distributed capacitors to a NEC2 model with LD cards (hook up one capacitor in the middle of each element.), but that is far too much money/trouble for most. More information on driving an array antenna can be found here: l Air Dielectric Patch   The obvious lazy solution is to accept the limitation and make an air dielectric patch antenna. An advantage of using air dielectric, is that the antenn

Weather Satellite Turnstile Antennas for the 2 meter Band

NEC2, 2 m band, 146 MHz, Yagi Turnstile Simulation and Build This article describes a Turnstile Antenna for the 2 meter band, 146 MHz amateur satcom, 137 MHz NOAA and Russian Meteor weather satellites.  Weather satellite reception is described here .  A quadrifilar helical antenna is described here .   Engineering, is the art of making what you need,  from what you can get. Radiation Pattern of the Three Element Yagi-Uda Antenna Once one combine and cross two Yagis, the pattern becomes distinctly twisted. The right hand polarization actually becomes visible in the radiation pattern plot, which I found really cool. Radiation Pattern of Six Element Turnstile Antenna Only a true RF Geek can appreciate the twisted invisible inner beauty of a herring bone antenna... Six Element Turnstile Antenna Essentially, it is three crosses on a stick.  The driven elements are broken in the middle at the drive points.  The other elements can go straight throug