I think that data backup is a system administrator's most important function.

You need to lose your data just once to convince you that I'm right.

My rules for backups

Your backup medium (disk, tape, etc) must be removable and transportable.

When evaluating backup solutions, remember that speed of disaster recovery is most important, followed by ease of following a backup routine. The last factor that you should worry about is media (tape, CD-R, disk) costs.

You must routinely verify that the data can be read from your backup tapes. Most backup programs allow a tape verification to be performed after each tape is written to. The downside is that it almost doubles the duration of the backup window and increases wear on the tape and drive. Whether you verify each backup, or only weekly backups, you must verify that your tapes can be read.

You'll need to decide whether your data is valuable enough to encrypt its backups. The downside to encryption is that at restoration time, you must know the password.

Why redundant hardware isn’t a substitute for a backup system

Maybe you think that because your programs and data reside on redundant hardware (read about RAID) that you don't need tape backup. Wrong. Redundant hardware protects you from hardware failure, but does not protect you from software failure.

Sometimes bad data, corrupted files, or program faults don't appear for days or weeks until someone tries to access them. Your redundant hardware won't help; you need to restore damaged files from a backup that predates the data corruption. No problem -- if you're following the grandfather - father - son - tape rotation scheme. So bite the bullet and stock up on tapes now.


You must keep some backups off-site,

to allow recovery in case your on-site tapes are stolen, crushed, flooded, or burnt to a crisp.

I recommend that you maintain three generations of tapes:


The sons are written to each evening, the fathers are written to each week, and the grandfathers are written to each month.

Sometimes the monthly and weekly tapes contain full backups and the nightly tapes contain just incremental or differential backups. Keep in mind that your goal is to recover from a disaster as quickly as possible, so maybe it makes sense to backup everything every night. Your mileage may vary.

Store your off-site tapes well away from your site. Many small businesses give their monthly backups to a manager to keep at home. Larger businesses contract with services that transport their off-site tapes to secure storage facilities.

As you put together a disaster recovery plan, plan on the worst-case. Don't assume that disks will always spin up or that you won't need to resort to a computer's humble diskette drive. Check yours now. I'll bet that most diskette drives in older computers no longer work . . . and good luck finding cleaning kits for them!

Why backing up files is necessary but not sufficient

Although up to date backups of your files are important, they're not sufficient to recover from a server system disk crash. In order to use your backed-up files, they must be restored to a working server, and if the server won't run because its system disk has died, you're still out of luck.

A recovery from a server system disk crash includes re-installing the server operating system (Unix, Windows Server, etc) -- if you have the server operating system's install disks and license numbers. If not, you're out of luck. (You may also be out of business.) You'll also need software drivers for any special hardware and then you'll need to configure them.

A faster alternative is to have a standby system disk ready for each server that is a bit-by-bit image of that server's system disk. When (not if) the server's system disk crashes, replace it with the standby system disk, then restore your data files from the lastest backup set, and you're back in business with a minimum of downtime.

Tape Libraries

Eventually, businesses outgrow hand-fed tape drives. The next step is tape libraries. (Visualize a jukebox that handles tape cartridges instead of records.) They're pricey, require tape library software, and take time to configure, but once in production with the right software, they handle the nightly backup chores unattended. Perhaps once a week or once a month, someone must attend to the library for an hour or so, to remove archival tapes and feed it fresh meat . . . er, tapes.

ADIC Scalar218 Tape Library