374 Technique 49: Getting Ready to Back Up Your Data

Optical media (CDs and DVDs)

CDs and DVDs might be the best backup media for the small network or single system user. They’re dirtcheap, durable, easy to use, and fast. They store forever (well, a long time anyway) and move easily from one machine to another. Most new computers come with a CD or DVD recorder, and if it’s not included, it’s easy to add at a fair price.

What’s the downside? A CD doesn’t hold very much data — 660MB or so. A DVD can hold 4.7GB. Is that a problem? Probably not if you’re backing up a single computer or a small network. Each disc holds enough data that you can most likely back up an entire system with just a handful of discs.

DVD recorders are just starting to show up in consumer-level computers, but you can easily add an external DVD writer, and the once-high price tags are dropping fast. A DVD holds considerably more data than a CD, so the time you can save in backing up makes the investment in a DVD recorder worth considering.

CDs or DVDs may not be the perfect storage answer for a large system, but for a single machine or small network, they’re great.

Online storage

Online storage services abound — just run a Google search, and you’ll find hundreds of them. The services range in price from free (for 5GB or so of backup space) to reasonable, and if you have a good (fast) network connection, online backup is a good choice. Online storage has the added advantage that your data is being stored at a different physical location from your home or business. If your building burns down, you know your backups are safely stored somewhere else. Of course, if you use an online storage service, you’re trusting them with your data — and it may be difficult to recover your data should the provider go out of business.

Online backup services offer the single user or small network administrator a user-friendly and secure

interface for quick updates to archive files. The administrator of a larger system will find convenience in scheduling whole-system backups for times when network usage is lowest. In either case, online services are friendly (usually), easy to use, and safe.

Choose a dependable service (preferably one that’s been in business for a while, with good references), with an interface that works for you. With a fast (and secure) connection, online storage might be the best choice for you.

Choosing an Archive Scheme

You can choose from three basic backup schemes: full, differential, and incremental. They each have advantages — some save restoration time, and some save media.

Cost, convenience, and time are the primary considerations when choosing an archiving scheme. For example, if you need to shuffle a lot of discs to do a full backup, run a full

backup once a week, and schedule unattended incremental backups on the days in between. Or, if you use a tape changer (or an online service), you can schedule a full backup every night.

Full backups

A full backup is just that — an archive that contains all the data that you want to save. You can create a full backup without archiving every program and data file on your computer; you can pick and choose only the files that you can’t conveniently re-create. What makes a full backup different from the other schemes is that you archive all the selected data every time you back up.

Differential backups

A differential backup saves only the data that changes from one day to the next. To build a differential backup set, you start each cycle with a full

Choosing an Archive Scheme 375

backup on the first day. Each backup after that is a snapshot of the changes made since the previous backup. Keep the initial backup and all the snapshots in a safe place in case you need to restore data. Every so often, start the cycle over again. The cycle always starts with a full backup.

You need at least two full sets of backup media to use incremental media safely so you don’t write over a backup that you may need to restore from.

To restore from a differential backup, apply the entire chain of archives, starting with the most recent complete backup and appending each snapshot in sequence. If the last full backup was a month ago and you back up daily, you’ll have 31 tapes in your archive to restore.

Incremental backups

To use an incremental backup scheme, take a full backup on the first day and then a differential backup on the second day. The second day’s backup includes only those files that have changed since the last full backup. The third day of an incremental backup scheme captures all file changes that have taken place since the last full backup.

Incremental versus differential backups

You may be thinking that an incremental scheme sounds suspiciously similar to a differential scheme. They are in fact very similar — each scheme archives only the data that’s changed. The difference is that a differential scheme archives the changes since the previous differential backup; an incremental backup archives the changes since the previous full backup.

Here’s an example:

1. You start with a full backup Sunday night.

2. On Monday, you create a new file named

/home/freddie/spybusiness.html. Monday

night, you create a differential archive that contains only the new file (spybusiness.html).

3. Tuesday morning, you create another new file named /home/freddie/gadgets.html. Here’s where the difference appears:

If you create a differential backup, Tuesday’s archive will only contain gadgets.html. (A differential backup archives the data that’s changed since the previous differential backup.)

If you create an incremental backup, Tuesday’s archive contains both files: spybusiness.html and gadgets.html (an incremental backup archives the data that’s changed since the last full backup).

You can see that an incremental backup scheme takes more media than a differential scheme. The big advantage of an incremental backup scheme (compared to a differential scheme) shows up at recovery time. If you need to recover from a hardware failure (or from a nasty typo), you only restore the latest full backup and the last incremental backup.

Having a backup plan

Formalize your backup plans and make them part of a routine instead of just performing a backup when you think you’ve accomplished something really monumental. Sometimes, truly monumental or important things go unnoticed until disaster strikes; unless you have a backup, you’ll lose a great piece of work. Make a plan and stick with it.

It’s not good enough to just have a backup plan. You also need to make sure that you can restore a backup if you need to. Don’t wait until the last minute to find out that your tapes are unreadable or that an online service is flaky. Test your media whether it’s on-site or off.

How often you back up is a decision only you can make, but consider how long it will take to reproduce the work lost if your backup routine is sporadic. Backing up is easy and painless, but losing a month’s work hurts.