The Backup Rule Of Three

The Backup Rule Of Three

Your data really isn’t safe unless you’re backing up properly and with lots of redundancy. The computer backup rule of three, also known as the Backup 3-2-1 rule, can help ensure that your data will last.

Photo by Jaymis Loveday

As Scott Hanselman points out on his blog, using just one kind of backup (eg, an external hard drive or SD card backup) is really not a backup. You need both off-site backup storage (eg, an automated cloud solution like CrashPlan), plus backups to different media types and multiple copies of everything you want to protect. Here’s the old IT rule-of-thumb for backing up:

Three copies of anything you care about — Two isn’t enough if it’s important.

Two different formats — Example: Dropbox and DVDs, or hard drive and memory stick, or CD + CrashPlan, or more.

One off-site backup — If the house burns down, how will you get your memories back?

The Computer Backup Rule of Three [Scott Hanselman’s Computer Zen]


  • Could not agree more.

    Unfortunately in my experience over many many years the issue of Data Backup is one of those things where most people are not interested, and they learn the lesson the HARD way when (not if) something fails and they lose irreplaceable data. Only then do they start asking the question “How can I make sure this NEVER happens to me again….” and they get on board with a robust 3-2-1 Data Backup strategy.

    Here is essentially the same message in more technical detail worth a read

    • if you’ve got something on a DVD & your DVD drive breaks, its a good idea to have it on a USB or external hard drive. or if your External hard drive croaks, its good to have it on a DVD etc.

      • While backing up DVDs makes sense, I don’t see how it applies to the “computer backup rule of three”. I’m wondering why I would backup my computer data to anything other than hard drives.

        All other consumer media is significantly smaller than HDDs which makes backing up a PITA e.g. backing up 1TB of data to DVD requires:
        – over 200 single-sided, single-layer DVDs
        – over 100 double-sided or double-layer DVDs
        – over 50 double-sided and double-layer DVDs
        – 40 single-layer BDs
        – 20 dual-layer BDs
        – 8 BDXLs

        These take more physical space than an HDD, perform slower, aren’t significantly cheaper, and are more likely to be superseded by a new format, so why would I use them for backing up?

        • coz hard drives die.
          they get damaged in floods. dvds dont.
          they’re affected by magnets. dvds arent.
          they get fried in power surges. dvds dont.

          if your data is valuable, the 5 mins it’ll take to write to the dvd is worth it.

          Edit: im not specifically in favor of DVDs or anything, but two formats is a good idea because different storage media break in different ways. & the chances of having more than one method of accessing your data breaking simultaneously is much lower than just one going.

          Edit #2: spelling

  • i have a home server i made from an old computer and it has several TB’s of data (Movies,music,pictures,software,documents) and as a backup i keep an offline mirror copy of that data when i buy new hard drives i buy two of them usually WD Green Drives and i put one in the server and keep one aside and once a week i run a mirror incremental backup but putting the offline drive in a docking station and copying over new or modified stuff to it then i disconnect the drive and place it back in the anti-static bag it came in and then place it in a foam cutout my local PC Store gave me which the hard drives were shipped in

    this give me two identical copies of everything now maybe 3 is suggested but as cloud storage especially on the scale i consume data space can be expensive and time consuming thanks to telstra my max upload speed is 100kb/s i would have to constantly be uploading my data to a cloud storage service 24/7 and eat up my data as telstra charge for uploads

    i might consider it when the NBN is connected and i can get like 40mbps upload but i have had this method for a couple years now and it seems to be working and i feel this method is safer than using a RAID setup also quicker and easier to restore in the event of a hard drive failure

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