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I run 2 LAMP web servers at different providers for disaster recovery purposes - a high powered live server, and a low powered backup server.

Currently I rsync all the data from the live server to the backup server once every 4 hours.

This works ok, but does spike system load whilst rsync figures out which files have changed.

Since all the websites also live in git repositories, I'm wondering whether a git push would be a better backup technique.

I'd have to include the live uploads folder in the git repo; and then the backup process would be:

live$ git add .
live$ git commit -a -m "{data-time} snapshot"
live$ git push backup live_branch

and then have a post commit hook on the backup server to checkout on every push.

Each website ranges in size from 50M to 2GB. I'd end up with about 50 separate git repos.

Is this a "better" solution than rsync?

  • Is git better at calculating which files have changed?
  • Is git push more efficient that rsync
  • What have I forgotten?

Thanks!

---- Data from some comparison tests ------

1) 52MB folder then adding a new 500k folder (mainly text files)

rsync

sent 1.47K bytes  received 285.91K bytes  
total size is 44.03M  speedup is 153.22

real    0m0.718s    user    0m0.044s    sys     0m0.084s

git

Counting objects: 38, done.
Delta compression using up to 4 threads.
Compressing objects: 100% (37/37), done.
Writing objects: 100% (37/37), 118.47 KiB, done.
Total 37 (delta 3), reused 0 (delta 0)

real    0m0.074s     user   0m0.029s    sys     0m0.045s

2) 1.4G folder then adding a new 18M folder (mainly images)

rsync

sent 3.65K bytes  received 18.90M bytes
total size is 1.42G  speedup is 75.17

real    0m5.311s    user    0m0.784s    sys     0m0.328s

git

Counting objects: 108, done.
Delta compression using up to 4 threads.
Compressing objects: 100% (106/106), done.
Writing objects: 100% (107/107), 17.34 MiB | 5.21 MiB/s, done.
Total 107 (delta 0), reused 0 (delta 0)

real    0m15.334s    user   0m5.202s    sys     0m1.040s

3) 52M folder then adding a new 18M folder (mainly images)

rsync

sent 2.46K bytes  received 18.27M bytes  4.06M bytes/sec
total size is 62.38M  speedup is 3.41

real    0m4.124s    user    0m0.640s    sys     0m0.188s

git

Counting objects: 108, done.
Delta compression using up to 4 threads.
Compressing objects: 100% (106/106), done.
Writing objects: 100% (107/107), 17.34 MiB | 5.43 MiB/s, done.
Total 107 (delta 1), reused 0 (delta 0)

real    0m6.990s    user    0m4.868s    sys     0m0.573s

4) 1.4G folder then adding a new 500k folder (mainly text)

rsync

sent 2.66K bytes  received 916.04K bytes  612.47K bytes/sec
total size is 1.42G  speedup is 1547.14

real    0m1.191s    user    0m0.180s    sys     0m0.268s

git

Counting objects: 49, done.
Delta compression using up to 4 threads.
Compressing objects: 100% (48/48), done.
Writing objects: 100% (48/48), 177.90 KiB, done.
Total 48 (delta 3), reused 0 (delta 0)

real    0m1.776s    user    0m0.390s    sys     0m0.497s

5) 1.4G folder - no change

rsync

sent 1.72K bytes  received 716.44K bytes  287.26K bytes/sec
total size is 1.42G  speedup is 1979.18

real    0m1.092s    user    0m0.168s    sys     0m0.272s

git

nothing to commit (working directory clean)

real    0m0.636s    user    0m0.268s    sys     0m0.348s

5) 52M folder - no change

rsync

sent 528 bytes  received 88.40K bytes  59.29K bytes/sec
total size is 62.38M  speedup is 701.41

real    0m0.779s    user    0m0.044s    sys     0m0.144s

git

nothing to commit (working directory clean)

real    0m0.156s    user    0m0.057s    sys     0m0.097s
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migrated from stackoverflow.com Dec 28 '11 at 0:26

This question came from our site for professional and enthusiast programmers.

2  
what about a "nice rsync" ? The system load spiking is exactly what you want: Finish the process AFAP, and this is OK as long as it doesn't interfere with the website's operation. –  Eugen Rieck Dec 27 '11 at 13:39
    
Thanks - I'm already doing a "nice rsync", which does help –  David Laing Dec 27 '11 at 14:23

2 Answers 2

up vote 1 down vote accepted

Actually I would suggest using a balanced mix of both. Your main backup should be committed (at least) every night to git. Sync it once or twice a week to another machine which is kept way far from the production box using rsync.

Git will help you with immediate recovery and it also makes analysis of data easier owing to the fact that you backup is version-ed and has a changelog. After any major change to the data, you can do a commit and push to git manually and put the reason in changelog. In case git goes bad then rsync will come to the rescue but keep in mind that you'll still loose data depending upon the frequency of rsync.

Rule of thumb: when it comes to backups and disaster recovery, nothing can guarantee to give you 100% recovery.

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Rsync is a wonderful sync tool, but you get a lot more versatility when running Git on the server(s), and pushing or pulling updates.

I have to track and backup user generated content on our server. The production server has a copy of the git repo, and every night it automatically adds and commits all of the new files via cron. Those are pushed to our gitolite server, which then uses hooks to sync the rest of the servers.

Since the servers have copies of the repo on-board, you get not only a snapshot, but detailed history information that could easily save you if anything happened to your server.

I think you pretty much have a good understanding of what both offer, I'd just change your line of thinking from servers checking out/exporting the codebase to just having their own repos. Another thought is that you could rsync your media files (you said 2GB for some of these sites, which makes me think there are a lot of media type of files?) and not track them in Git.

share|improve this answer
    
I've added some performance data; which shows that rsync is nearly always faster than git. However, I like your points about the extra power of having git repos on the live server - I'm wondering if a hybrid approach isn't best, with changes being pushed into the git repo, and then git repos being rsynced to the backup server... –  David Laing Dec 28 '11 at 0:58

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