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Back It Up!

"Save Early, Save Often"

By Theo Gantos

One of the most difficult concepts for people to grasp about technology is the need for backup systems. We always think “it won’t happen to us”, someone else will have the disaster. A few years ago I had a teary-eyed grad student at Northwestern come to me holding a old dog-eared floppy disk. She said it had her 400 page dissertation on it, which was due in one week, and now it was getting a disk error. I asked her where was her backup copy? She said, “What’s a backup?”. We got about 300 pages back but she had to scan in the other hundred. She got religion about backups after that experience. An old IS quip offers this definition, “A backup is something users make the day after their hard drive crashes”.

You can’t predict disasters. However, you can survive them. Your chances are much better if you are prepared. Having a sound backup strategy will greatly increase your odds of surviving these events. Others have traveled down this path before, so don’t experiment with your own system unless you know what you are doing.

A backup is a method of preserving information critical to your operations in the event of a catastrophe. What kinds of catastrophes? Lightning, fire, floods, theft, vandalism, all qualify. The more layers of defense you have against these, the better your odds. Backups are copies of information. How many you have, how they are made, and how they are stored makes the difference.

The best backup medium is non-magnetic, i.e. CDROM or magneto-optical disk, lasts more than 10 years, but it is costly (per megabyte) and slow. The most cost-effective choice is magnetic tape, (in order of reliability: DLT, 9 track, AIT/4mm DAT/8mm) good for several (5+) years. A (sealed) hard disk can store data for several years reliably. If you are lucky, removable hard disks (syquests, jazz,etc) will last a year or more without errors. Finally, the non-rigid media such as Zip disks and regular floppies can be relied on for data retentions of up to 3-6 months.

The ultimate in reliability is to use the media only once coupled with making a new backup each day. Often this is unnecessary, since weekly cycles areadequate for most applications. Longer than one week per set is unwise; an entire month on one backup set is usually just too much to risk. Tapes can snap, disks can get spilled on, etc. If you keep 3-6 months of weekly backups and another 12-18 sets from each month beyond that, you should cover files up to two years.

I recommend for most businesses to get a 4mm DAT DDS2 tape drive with the SCSI interface (about $1000) and use Retrospect software from Dantz Development, which provides network backup capability for both Windows and Macintosh environments. One tape can hold about 5,000 to 6,000 (5-6GB) megabytes of info. If 6 GB per tape is too small, I recommend using a Digital Linear Tape (DLT) drive. These go up to 70 GB per tape and stack loaders are also available to switch between tapes automatically. Retrospect is especially good because it has the option to compare files and only backup redundant files once, thus saving space. It keeps a record of where all these copies are on it’s “snapshot” so the files can be restored from the single copy automatically. 90 meter DDS DAT tapes are under $7 in quantities of ten or more. If you use one tape per week, 26 weeks would cost you under $250. In addition, another 18 tapes for the full 2 year period would be under $200. That’s under $450 for a great strategy that’s probably 99.99% effective. You should write the date of purchase on each tape. I would discard tapes after two years to be safe. Reusing is not a great idea, since tapes get less reliable with each use. The point of the whole investment is wasted unless the data is there when you need it. I usually make single backups of critical data such as accounting and have 4-6 sets. I rotate these until the two years are up and then buy another set for this purpose. Your annual costs for this should be under $300, depending on how many tapes it takes to backup all your data. When people lose their hard drive, they often pay emergency services more than $1,000 to attempt to recover the data which often cannot be retrieved so $300 is cheap insurance.

Here’s how the strategy operates. First, each week (usually on Monday) you use a new tape, and make a “new” backup under Retrospect. Label the tape and date it (important!). This starts a new catalog and “set”. Make sure you use a “compare” pass to recheck what was written on the tape with the source before you archive it. Then each night, run a “normal” backup (otherwise known as an incremental backup), follwed by a compare. This copies only the files which changed since the “new” backup. On the next Monday, you repeat this process, removing the old tape and storing it in a safe place. Continue this until you have from three to six months of weekly backup (more is better). For tapes older than the weekly retention (older than 3-6 months) take the first weekly of the month, then keep it for a total of two to three years or longer as your needs require. Recycle the remaining tapes from that month back into the weekly cycle. Don’t erase the initial use date on the label. When the initial use date is beyond two years old the tape should be discarded and not reused. Critical files such as accounting data can also be backed up during the day, right after they are used, to their own tape.

Storage of your backups is also very important. I recommend that you only keep your current weekly backup onsite in a fireproof safe. Most fireproof safes will NOT protect your tapes from the heat of the fire unless they are the data-rated four hour type. Normal fire-proof safes are meant only for documents, which burn at a higher temperature than tapes melt at. The rest of your backups should be kept offsite in a fire and magnetically shielded vault. Then they will be protected in case you ever need them. DON’T put them in the box under your bed at home.

Using this procedure, you should be in a position to minimize your loss of data to about 1 day in the event of most disasters. Don’t wait until the day after the disaster to get religious about backups.

Theo Gantos is president of TEKA, a technology consulting firm. Contact him: