In the old days, I had a simple batch file that pkzipped all my data files into an on-disk file suitable for archiving. Then I realized that was like saving your flammables in the fireplace, so I backed it off to tape once we could afford one. Too cumbersome, and too many failures (you don't discover this until you try to restore!). I went both the dual hard drive route (no good on power supply disasters) and the floppy disk (!) route (very time consuming and media consumptive, even back then). Through it all, I considered the issues of optimization and convenience. I decided that, once I had installed a network, the right way to do it was to back up every machine on every other machine - but only the data, not the applications. That was still time consuming with 10Mb ethernet (more so with our first Arcnet network), but came into its own once I switched to 100Mb. It's what I use now. The rationale has proved a comfortable balance. I simply copy, from each computer, the contents of the My Documents folder to a dedicated, self-descriptive subfolder (Sandy's docs, Jamie's docs) located outside that computer's My Documents (e.g., to C:\Backups) folder. When I install applications, I change the default locations for their data to a subfolder in My Documents. I manually copy the AOL Organize folder to keep the e-mail files for each person to their My Documents folder before kicking things off. This process:
1. Minimizes the amount of data to be copied over the network and speeds the backup process.
2. Keeps multiple copies of backups for each machine on the network on other machines and readily available.
3. Allows me to make off-site removable media copies from the machine with the biggest removable storage device.
I used to compress the backups using PKZIP before copying to further condense the data transferred, but this lowers reliability (1 bit error could make the entire backup irretrievable, rather than just the file involved), so I stopped when media got cheap.
Cost? The footprint on each hard drive of the My Documents folders. At $.30 to $.50/Gigabyte, the cost is non-recurring (see reuse below) and trivial. Anyone filling up their hard drives lately? In the original backup batch file that I wrote long ago, I used XCopy with the switch that only copied changed files, and then inverted the archive bit so that file wouldn't be copied again unless subsequently changed (Xcopy /m /s /v). Don't know how to do this anymore in XP, but it would be nice. Not much of an issue, because I run the backups overnight, with all computers running at once - they cooperate just fine on the network - so it really doesn't matter how long it takes.
By alternating the subfolders each backup cycle, you have two or more (your choice) backup versions on line at once, and just delete the contents of the oldest backup folder when you come full circle, thereby reusing the footprint.
I do make the occasional DVD copy (bought 50 media at Staples this week on sale for $7.94 plus tax - <$.16 each), and will move to double layer when media prices drop. I do this so that I can carry a copy in a laptop bag in case I need to refer to a file when away from home.
This may not work well for people with large media collections, but I only have about 9GB of MP3's, a few JPEGs of family photos, and no MPEGs. Of course, drives are getting bigger, Gigabit ethernet getting cheaper, and Blu-Ray is coming. Check your space requirements (in Explorer, right click My Documents and click properties); you might be surprised at how little (data, that is) you really have to back up. If you do the math, 4 or 5 GB of data moves across a 100 Mb link through a switch at about 2 to 3 megabytes a second (drive, processor, etc. dependent) so you can easily run two or three machine backups simultaneously in about 20 to 30 minutes, unattended. Overnight, it's no sweat. Even an 802.11G link will work reasonably well. Only occasionally do you get a snafu, and then you just restart that copy and have a cup of coffee.
You may take issue with the idea that I'm only backing up data and not applications and OS. I am happy with that idea, because by the time a backup is needed because of hard drive failure, it is long overdue that the OS be reinstalled to get the Registry back to manageable size so Windows startup completes before closing time, and kill off those nasty bits of viral/adware/spyware/trojan crud that choke the machine anyway. I do this periodically just to bring the machine back to original speed and responsiveness; I look on it as the digital equivalent of an oil change.
I realize this is not a universal panacea, but for some, it's handy. Your mileage may vary.