Mastering UNIX® Shell Scripting: Bash, Bourne, and Korn Shell Scripting for Programmers, System Administrators, and UNIX Gurus, Second Edition

CHAPTER27

Using Dirvish with rsync to Create Snapshot-Type Backups

Six months ago I hadn't heard of Dirvish and I had used rsync fewer than 10 times. Now when I need to copy files either locally or over the network, I like to use rsync for its compression capabilities and, after an initial copy, the ability to replicate only changes in a file as opposed to changed files. Usually when a file is modified it is only a small percentage of the file that has changed, so sending only the updates greatly reduces the amount of data transmitted over the network. We are able to do this feat because of hard links and inodes. Read on; this is a very beneficial chapter for any shop, and it's free!

Dirvish is a backup program, originally written by J.W. Schultz, that you can download from www.dirvish.org. Dirvish uses rsync to transfer files over the network, and thus uses the rsync remote-update protocol, which allows us to do an incremental backup by transmitting only the changed parts of the changed files, as opposed to a tape incremental backup that requires transmitting the entire contents of all changed files. We studied rsync in detail in Chapter 7, “Using rsync to Efficiently Replicate Data.”

The Dirvish backup program uses one or more backup servers with the image data stored on disk. Ideally, this backup server should be located in another building, or location, and then we have offsite backup storage. You may still want to make periodic backup tapes for legal purposes on a monthly ...