How To Back Up Your Personal Computer

 

 

January 30, 2008

(Updated 31-Jan-2008, 7-Feb-2008, and 8-Feb-2008; updates in red)

I've read countless articles about backup over the years, but not one of them approached the problem properly. They all focus too much on hardware and software, and not enough on what I call independence—getting the copies and the originals separated so they're not subjected to the same threats. And, too often they deal with just one or two threats, most commonly a disk crash, and ignore the others. In fact, not one article even bothered to enumerate the threats to help check that the backup plan deals with each one of them.

I've been thinking for nearly a year about writing my own article that would set matters straight, and now it's time. I blogged a bit about backup last August and promised more; what you'll find here is much more.

I'll cover the principles of backup, list the threats to your data (there are six of them), describe the specific hardware, software, and online facilities available for Windows and OS X, and then outline some specific backup plans. My focus is on personal-computer backup rather than servers or mainframes, although the principles apply universally. Also, I only briefly touch on data privacy (preventing unauthorized use of data); unfortunately, backup usually reduces data privacy, since the more copies there are the more opportunity for someone to gain access to one.

Here's a detailed outline:

What is Backup?
Threats to Your Data
The Perfect Backup Solution
Protecting Against Threats
Planning for Backup and Restoring
     Convenience vs. Independence
     You Need a Backup Plan
     You Need a Restore Plan
Backup Hardware
     FireWire and USB External Drives
     Network Attached Storage (NAS)
     RAID
Backup Software
     Minimum Requirements for Backup Software
     Encryption
     OS X: In-the-Box Backup Software
     OS X: Add-On Backup Software
     Windows Vista: In-the-Box Backup Software
     Vista and XP: Add-On Backup Software
Online Backup Services
Dealing With the Threats
     Backup for User Error, Computer Failure, and Disappearance
     Backup for Surge
     Backup for Office Destruction and Regional Disaster
My Backup Plan
Evaluating Your Backup Plan

There are some links below to Amazon. If you click on one to buy anything, it won't cost you extra, but I get a fee from Amazon.

Disclosure: I have done some consulting work for Microsoft, and some of that work had to do with storage systems, although not with backup directly. As you will see as you read below, I don't think that association biased my conclusions.

What is Backup?

A backup is a copy of data that is sufficiently independent of the original so that destructive events can't affect both at the same time. Backup doesn't prevent destruction of data; it only allows you to recover the data once the destruction has occurred.

A simple example of backup is copying files from a laptop to a CD (the act of copying), putting the CD in your desk at home (independence of location), and having the laptop stolen (the destructive event). Since the CD wasn't stolen, you still have the data that was copied to it. Sure, your laptop is gone and maybe sensitive information has fallen into the wrong hands, but at least you still have the data you saved to the CD. (You cover loss of the laptop with insurance, and you protect sensitive data with encryption, but those subjects are outside the scope of this article.)

To design and implement a backup plan one has to consider the possible threats to data (e.g., theft, electrical surge, fire), the various ways to copy data (e.g., using the Mac Finder or Windows Explorer, using a backup utility, using CD/DVD-burning software), and ways of achieving independence (e.g., online storage, placing media in a safe-deposit box).

Unfortunately, nearly all articles about backup focus on the copying, and ignore the other two (threats and independence). But without evaluating all the threats, there's no way to be sure that the backup will allow you to recover from them, and insufficient independence means that both the data and the backup can be destroyed by the same event. An obvious example is a fire that destroys everything in an office, including any backups kept there.

Additionally, if backup isn't convenient—automatic, ideally—it won't get done often enough to be effective. (It's common after a data loss for someone to regret that their most recent backup is months old.) Restore has to be convenient, too, or else the damage will be compounded. An electrical surge is bad enough, but if your data is unavailable for a week while you restore it from an online service, you still lose a week of productivity.

Since backup is potentially expensive and time-consuming, you also have to consider the importance of your data. Backing up irreplaceable photographs is more important that backing up application preferences, and backing up browser caches or temporary files isn't important at all.

Threats to Your Data

There are only six types of threats that can destroy data:

1. User Error. A user mistake that accidentally deletes or overwrites one or more files. I recently overwrote an image file with a cropped version of the image, but was able to get the original back in a few minutes from the ongoing backup kept by OS X's new Time Machine.
2. Computer Failure. This includes any failure of hardware or software that results in data loss. I put the two together because it's often difficult to tell whether the problem was caused by software or hardware and because the effect on the data is usually the same. The most talked-about failure, a disk crash, is in this category, but so is an OS upgrade that causes a file system to be corrupted or an application install that deletes data files. (Apple once accidentally released a version of iTunes that could delete all files on a hard drive.)
3. Surge. Electrical surge is in its own category because it can affect every plugged-in device in a home or office, so it makes independence especially difficult. Copying data to an external drive won't protect you from a surge if the drive is plugged in, but if it's not plugged in you can't access it. A good surge protector can prevent damage from some surges, but there's no device that's guaranteed to prevent them all.
4. Disappearance. This includes burglary, robbery, theft, and accidental loss (leaving a laptop in a taxi). The good thing about theft and loss is that even the slightest amount of independence is effective: Thieves might take the computer on the desk, but probably won't notice the hard drive on a shelf under the desk, and someone who snatches your laptop in a train station probably won't take the USB flash drive in your pocket.
5. Office Destruction. This includes anything that destroys the location containing the computers and includes fire, explosion, structural collapse, collision, water damage, and vandalism. Everything in the office might be destroyed, including external drives and CDs/DVDs.
6. Regional Disaster. Anything that damages an entire neighborhood or city, such as radiation, flood, earthquake, tornado, and various acts of war or terrorism. Here even a copy in a bank safe-deposit box may not be safe.

The Perfect Backup Solution

The almost-perfect solution is to back up your entire computer every hour to an ultra-reliable, redundant, online storage service such as Amazon's S3. I say "almost" because the backup software you use might have defects. To make it perfect, you need two or more completely independent copying utilities and services.

Unfortunately, there's too much data. For example, if a photographer comes back from a shoot with 20GB of photos (not unusual) and has a T1 line (1.544 megabits per second) operating at 100% efficiency (extremely unusual), it would take 29 hours to copy the photos to an online service. Every 1GB of image data modified (50 photos at 20MB each) would take an additional 1.5 hours or so to upload. That's assuming that there is a T1 line, that it operates as 100% efficiency, that the line isn't being used for anything else, and that the online services can receive and store the data that fast. At a more realistic upload speed, say 500 kilobits per second, it would take more than 3 days to upload the 20GB, by which time the photographer might have shot another 60GB. The backup would never finish.

Oh, I forgot... the photographer needs 2 T1 lines, because we were going to use two independent services.

So, the problem with the perfect backup scheme is that it won't work. We need to back up to hard drives and/or optical disks, and that gets very complicated, as you already know.

Protecting Against Threats

The purpose of backup is to recover from damage, not prevent it. Still, it makes sense to reduce the likelihood of damage occurring; restoring is always a chore, and you still have to replace the damaged or stolen equipment. Think of protection as reducing the probability of a restore, rather than reducing the need for backup.

Here are some things you can do:

• Connect your computers and external drives to a surge protector. The good ones cost a few hundred dollars. I suppose cheap ones are better than nothing, but it makes no sense to protect $5,000 worth of equipment with a $29 power strip.
• When you're traveling, never let go of your laptop. I take mine into restaurants and while I'm eating I sit on the shoulder strap. If you have to leave it in an office, use a cable to attach it to the desk. This will at least delay a thief for a minute or two, and maybe he or she will decide that's too long.
• Build a shelf under your desk and put external drives there rather than on the desk. (If you put them directly on the floor they'll be knocked about by the cleaning staff.) If you put them in a drawer, make sure there's enough ventilation. Network-Attached Storage (NAS) devices are especially useful here because you can put them far away from your desk.
• Don't work in an apartment or condo, especially if it's not sprinklered. In my town there's a fire in a condo about once a year. The last one was started by a cigar left in a planter on a deck, with some firewood and four 20-pound propane tanks nearby (lots of barbecues, I guess). It destroyed 36 units. The newspaper didn't report how many computers, external drives, optical disks, and USB drives were melted, burned, or soaked from fire hoses.
• If your home or office is sprinklered, make sure your computer, or at least your external drives, are covered so they don't get wet.
• Keep any offline media or devices in a fireproof media safe. These aren't ordinary office safes, not even ordinary fireproof safes, but special safes designed for tapes and CDs/DVDs. I use them for hard drives, too. I have have both a Sentry Model 1710 and a 6720. One is in the basement and one is right next to my computer so it's easy to access. It doesn't replace off-site storage, but it's better than keeping media and devices loose on your desk.

As I said, even if you do any of the above, it doesn't allow you to get away without backups. It just lessens the chance that you'll need them.

Planning for Backup and Restoring

Convenience vs. Independence

Generally, the more convenient a back up method is, the less independence you get. So, you'll need a combination of methods: One or two that are convenient but provide just enough independence to protect against the most common threats, and one or two that are inconvenient but which provide complete independence.

For example, using a background backup utility like Apple's new Time Machine, available with OS X 10.5 (Leopard), is convenient, but since the backup drive has to be within WiFi range and plugged in to power, it doesn't provide enough independence to protect against Surge, Office Destruction, or Regional Disaster. But, since those attacks are so much less common than User Error, Computer Failure, and Disappearance, running Time Machine is a great idea. It's just not the only idea.

For protection against surge, all you need to do is back up to an external disk (probably not with Time Machine) that you can unplug and, for good measure, put into a fireproof media safe. Store that drive in a neighbor's house and you'll protect against Office Destuction as well. Take to your mother's house 25 miles away and you're protected against most Regional Disasters. Copy your irreplaceable files, such as photos, to Amazon's S3 and you're even more completely protected.

You Need a Backup Plan

The way we arrived at the combination of methods in the previous section was to list the six types of threats, list the available backup methods, and then pair them up to ensure that we were covered. The more backup methods available and the more you know about them, the more effectively you can come up with something you can live with. If your plan is too inconvenient, you'll find you're not using it, and then you won't be protected.

As I'll explain below, neither Windows (even Vista) nor OS X comes with sufficient backup software, so you'll need to buy a third-party utility.

You'll have to spend some money, mostly for software and external drives. The software will cost less than $100, a couple of 120GB drives for your most important data will cost about $100 each, and each 500GB drive will cost less than $200. Amazon's S3 service is really cheap, only a few dollars a month. So, for about $500, a little planning work on your part, and a slight change to your work habits you can get almost 100% protection from the six types of threats.

You Need a Restore Plan

It's a safe bet that very few people who do backup have ever tried a restore to see if it works. And, it's not hard to see why: Restoring a complete system is pretty disruptive, and if it doesn't work you will have just wiped out a perfectly good system. You have to put another hard drive in the system so you can safely overwrite it, or wait until you have a new computer. (I have a Windows desktop with six drive bays with handy slide-out trays, so it's very easy to pop in a new drive to test a restore while the primary drive is safely out of the the computer. But my desktop is very unusual, and it's more common today to see computers getting smaller and even more closed up.)

Even without actually doing a complete restore, you should spot-check the backup to ensure that your files are really there. Backup software that won't let you do this, such as Vista's Complete PC Backup, should be avoided.

Your restore plan also has to include a way to replace damaged hardware. If you live near computer stores and they're open when you need them, you might be able to just go out buy what you need when you need it. But if not, and time-to-restore is important, you'll have to have replacement equipment on hand. The equipment really has to be available—if the replacement hard drive has data on it, you won't be able to use it without destroying that data.

After a restore, make sure you don't start running without a backup. For example, suppose you keep a complete, bootable copy of your primary drive on an external drive. If the primary drive fails, you can boot from the external drive, which gets you up and running immediately, losing only a few hours of work. But, if you run that way, you no longer have your backup, since the backup drive has become the primary and the old primary is dead. Instead, you should immediately clone the backup to a replacement primary drive or, if that's not feasible, clone the backup to a second external drive.

Backup Hardware

While you'll sometimes back up to CDs/DVDs, flash drives, or to an online service, because of the amount of data to be backed up you'll more often use a hard drive. The main choices are a single external drive, a network-attached drive, or a RAID drive (which could also be network-attached). Internal drives aren't good choices because they're not sufficiently independent of the computer being backed up. They're gone if the computer is stolen, and they share the same drive controller, so a controller failure could destroy the data on all the internal drives.

FireWire and USB External Drives

These drives are great choices for backup. They're available in sizes from about 100GB to 2TB, and some of them are even entirely powered from the USB cable, which makes connecting them and transporting them especially convenient.

If the drive is going to be running all the time, put it out of sight, such as on a shelf under your desk, or on a bookshelf with some books or a family photo in front of it. Figure that a thief won't know your drive is even there and, even if he or she does, nobody wants to heist a $200 drive when there are computers, CDs, and jewelry to take instead, all much easier to fence.

Network Attached Storage (NAS)

This is a fancy name for a drive connected to your local network instead of directly to a computer. NAS has been around for years, but only recently have devices been created for home and small-office users that are cheap and easy to set up.

The best-known new NAS device is Apple's new Time Capsule, which is a 500GB or 1TB drive combined with a wireless base station. It allows you to back up, with or without Time Machine (OS X Leopard's built-in backup software), to the drive wirelessly. This means it can be farther from your computers than a directly-connected drive, such as in a closet, on a high bookshelf, or in another room. (Friendly neighbors might even be able to put their Time Capsules in each others' houses, although I haven't tested that arrangement.)

One popular form of NAS is another computer on the network, connected with WiFi (like Time Capsule) or wired. But another computer is much more expensive than just an attached drive, requires much more power and space, and introduces another machine to be set up, booted, maintained, and possibly even backed up. A little box you can just attach and forget about is what's really needed.

To find NAS boxes, go to Amazon and search for "nas drive", "nas disk", "ethernet drive", or "ethernet disk". You'll drives with network attachments, drive cases with network attachments (you have to add the drive), cases with WiFi and with and without drives, and even cheap ($85) devices to which you can attach a USB drive. Here are some examples, none of which I'm recommending, as I haven't tried them:

Some things to watch out for when you buy an NAS device:

• Other than Time Capsule (which also works with Windows), even the easy-to-set-up devices can be complicated to set up. If you're used to setting up networks, downloading drivers, and dealing with strange preference dialogs, you'll be OK.
• Some backup software organizes the entire backup as a series of giant files (>4GB), and some NAS drives don't allow files greater than 4GB, so you may have a problem.
• According to reviews on Amazon, some of these devices are very slow.
• Some devices won't work with a Mac and those that do might not work with OS X 10.5 (Leopard).
• Even if they will work with a Mac, they won't work with Time Machine because it doesn't support networked drives (other than Time Capsule).
• Apple's AirPort wireless base station has a USB port for an external drive, so you might be able to use that instead of getting a Time Capsule.

RAID

RAID stands for Redundant Array of Inexpensive Disks. The problems with RAID are that it costs extra for the same amount of storage (at least one extra disk and some fancy electronics) and that the disks aren't nearly independent enough.

There are various RAID arrangements, the two most popular of which are RAID-1 (mirroring) and RAID-5 (striping with parity). The idea is that, if a disk fails, it can be removed from the running system and replaced without the system going down or any data being lost. When you replace the defective disk, the RAID system automatically restores, over a period of hours, the data that was on it. (So-called RAID-0, also called striping, isn't really RAID at all because there's no redundancy. The loss of either disk destroys all the data on both disks. RAID-0 is for performance, not for reliability, which is actually reduced.)

RAID is OK is you're using it to replace what otherwise would be a single drive (primary or backup), but it doesn't substitute for backup. Moreover, if your budget is limited, the extra money you spend on RAID might mean that you have less to spend on backup.

To see why RAID doesn't diminish the need for backup, we can do a quick threat analysis, as we do for all other backup methods:

1. User Error: No help; with RAID there's still just one copy of the data.
2. Computer Failure: RAID protects only against disk failure. That's probably the most common hardware failure, but as RAID doesn't protect against other hardware failures, such as the RAID controller itself and the rest of the computer, nor against software failures, the need for backup hasn't changed.
3. Surge: No help, as all RAID hardware has to be plugged in.
4. Disappearance: No different than a single disk. An external RAID cabinet can be hidden below the desk, but so can a single-disk cabinet.
5. Office Destruction: No help.
6. Regional Disaster: No help.

Anyone who thinks RAID provides sufficient protection is focused too narrowly on a single kind of failure, the disk itself, and is ignoring the other threats.

Backup Software

OS X and Windows come with backup software, but it's insufficient because either it's inconvenient and error prone (on OS X, without third-party software, the only way to copy files to an removable drive is with the Finder) or because it doesn't meet what I consider the essential requirements for backup software. I'll review those requirements and then briefly review both the backup software that comes with OS X and Windows ("in-the-box") and what you can buy from a third party.

Minimum Requirements for Backup Software

The following requirements must be met by any backup system:

1. There must be a way to determine what will be backed up. Systems that tell you they're backing up "other files" without telling you what those are, like Vista's Back Up Files, are unacceptable.
2. There must be a way to tell if a specific file was backed up, so you can spot-check the backup. Systems that keep the backup in a mysterious form (e.g., some giant compressed file) don't meet this requirement unless they also have a user-interface for showing you a list of files. Vista's Complete PC Backup fails in this regard (more later).
3. There must be a way of verifying the integrity of the backup, short of doing a restore and running the system for a month or two to see if any hidden problems show up. A system that uses the ordinary file system meets this requirement, because you can run a utility or script to compare to two folder hierarchies, file-by-file if you want. Systems that use their own format have to provide a separate verification option.
4. For a complete backup, there must be a way to restore individual files. (This may not be a requirement for you, but it is for me.)

Encryption

As I said at the start, I'm not going to say much about data privacy (e.g, preventing identity theft), except to note that backup makes the problem worse.

However, many backup programs provide a way to encrypt the backup data, and that's what you should do. If your backup utility doesn't provide encryption, you may be able to encrypt the data anyway by encrypting the volume the data is written to. On a Mac, you can use Disk Utility to create an encrypted disk image, as I explain here. (8-Feb-2008 update) I'm not sure the method in that article is practical. I've updated the article to explain why.

OS X: In-the-Box Backup Software

OS X 10.5 (Leopard) comes with only one backup program, Time Machine, and it's a great one that everyone should use. The previous OSes didn't come with anything, although there was always a way to burn CDs and DVDs and to copy files with the Finder.

OS X: Add-On Backup Software

If you subscribe to Apple's .Mac online service you can download a backup utility called Backup. It's primary purpose is to back up online, but you're supposed to be able to use it to back up to external drives and CDs/DVDs. The one time recently when I used Backup to back up to DVDs, it failed.

A much better choice is Super Duper. I've used Super Duper to make both bootable disk images and partial backups for carrying offsite, but haven't been able to for a few months because it doesn't work with Leopard yet. (It does now.)

I also used iBackup before I got Super Duper, and it seemed to work fine, although it won't back up a complete system like Super Duper will.

I've tried Retrospect for the Mac, which interested me because it's one of the few backup program that can write CDs/DVDs, but it repeatedly hung trying to write a DVD.

I've just written my own utility to copy folders and files to multiple CDs and DVDs, SpanBurner ($10).

Windows Vista: In-the-Box Backup Software

I'm not going to discuss the backup software that comes with XP because (1) with one-exception, noted below, Vista's software is much better, and it's unacceptable, and (2) Vista has been Microsoft's current OS for over a year.

Vista comes with four backup systems:

1. Vista Business, Ultimate, and Enterprise include Complete PC Backup which, near as I can tell, works perfectly. The unfortunate thing about it is that it writes everything to a VHD (Virtual Hard Disk) file, so you can't directly examine it to reassure yourself that it worked. You're supposed to be able to open a VHD file with Microsoft's Virtual PC (a free download), but I couldn't get that to work (weird error messages). Some people have reported success in taking the VHDmount command from Virtual Server (separate download and install) and running it on Vista (or maybe XP), but I didn't try that.

   (31-Jan-2008 update) I don't think I was right about Virtual PC; mounting a VHD isn't something it's supposed to do, near as I can tell. But, I did install VHDmount by downloading Virtual Server (free), choosing to custom-install it, selecting only VHDmount to be installed, and then running VHDmount on the VHD file written by Complete PC Backup. Worked perfectly. So, if you're willing to install and use VHDmount (you don't have to use Virtual Server, or even install the whole thing), there is a way to verify that your backup was written and to restore individual files.

   Complete PC Backup doesn't have a built-in scheduler, but you can schedule it from the Task Scheduler, which is on the Administrative Tools menu. Choose Create Basic Task, enter a name and set the time, enter "wbadmin" for program, and "start backup -backupTarget:F: -include:C: -quiet" in the arguments field, assuming you want to back up drive C to drive F. On the next panel check "Open the Properties dialog for this task when I click Finish" and, when it opens, check "Run with highest privileges".

   To my way of thinking, even though Complete PC Backup seemed to work (I never tried a restore), that ordinary users (who don't install VHDmount) have no way to check its output is a serious defect. Also, and probably for the same reason, you can't restore individual files; you can only use the VHD file, all of it, during a fresh install. So, it fails my Minimum Requirements for Backup Software (see above), unless you install VHDmount.

2. All versions (I think) of Vista come with Back Up Files, which allows you to back up various categories of files (e.g., pictures, music, e-mail) to drives, CDs/DVDs, and across a network. There's no information about what actually gets backed up, but there is a statement that if you check "Additional files" you get more. You have no idea whether your Wiggly Write or Dipsey Doodler application files are going to get backed up. When someone complained on an online forum to Microsoft, the response was that they could ZIP the questionable files first, since ZIP files are backed up. They rightly responded that this was beneath stupid.

   So, Back Up Files fails my Minimum Requirements for Backup Software. (I still use it because my computer happens to have four mostly unused drives inside it, but I don't count it as part of my backup plan.)

   With the more advanced versions of Vista, you can run Back Up Files automatically according to a schedule you set.

3. System Restore can prevent against some User Errors and Computer Failures. It takes a snapshot so your system can be rolled back to a previous point. Only system files are backed up—no user data. It's nice to have, but doesn't address the real problem, which is loss of your own data.
4. Previous Versions uses a part of each drive to keep past versions of files that are changed, as many as will fit. There's no way to expand the allocated space or to keep the versions on an external drive. Also, you get versions only as far back as the most recent Back Up Files backup, which is listed among the versions. I'm not sure what happens if you've sent your Back Up Files drive elsewhere.

   Previous Versions provides substantial protection against User Error if the good stuff was from yesterday, since you only get one version per day. If it was last week, you may not have it. Contrast this with Time Machine, which keeps hourly backups for a day, daily backups for a month, and weekly backups forever, space allowing. All on an external drive. And, it's the entire system, not just user files that have changed. And, you can restore an entire system from the Time Machine backup.

So, while Vista has four backup systems, even all of them used together don't provide protection from the six threats. Each of them has serious flaws:

1. Complete PC Backup provides no way to verify its output or to restore individual files, unless you install VHDmount.
2. Back Up Files doesn't back up all files, and won't tell you which it will back up.
3. System Restore doesn't do anything with user files.
4. Previous Versions is only once a day, is limited in how far back it goes, and can't write to an external drive, which means there's no independence from the main drive.

All of the Vista back up systems use the Virtual Storage System (VSS) to ensure that only internally-consistent files are backed up, even if an application has them open. OS X doesn't have anything like that; their thinking is that Time Machine will get the file next time. None of my disparaging remarks are intended to disparage VSS, which is an excellent piece of work.

I have heard that XP lacks most of the four backup systems in Vista, but that there is a backup program, not installed by default, that works better than Back Up Files, in that you can at least tell it what you want backed up.

Vista and XP: Add-On Backup Software

This field is so vast and rich that I wouldn't know where to start, so I'll just make two general comments:

• You can get anything you want from a third-party, including bootable complete backups, incremental file backups, online backups, whatever.
• What you can't get is anything wired deeply into XP or Vista that works as reliably and as smoothly as Time Machine.

For years I used Retrospect on Windows, and it ran reliably. I can't say for sure that it would have restored my entire system, because I never tried it. When I spot-checked for files on the backup, they were always there.

Online Backup Services

I dismissed online backup earlier because it wasn't perfect, but that doesn't mean it's not a good idea, especially for your most important data, such as irreplaceable digital images.

A widely-used Apple online backup service comes with .Mac. You use the Backup utility, which I mentioned above.

Unfortunately, in two years of trying I have never gotten Backup to work reliably with .Mac, so I don't recommend it. The problem is that when I set it up it runs OK for a few days, then quits with absolutely no notice whatsoever (other than an obscure log entry in a place I never look), and I have no idea how to get it started again. Most recently, with over 20GB free on my .Mac account, it quit claiming it was out of space. As I mentioned above, I haven't gotten it to back up to DVDs, either.

.Mac also comes with a virtual online disk, called iDisk, which you can read and write like an ordinary disk, only much slower. I have had some success dragging things to iDisk with the Finder. I've also used Transmit to create a droplet that sits on my dock. Any files or folders I drag from the Finder to the droplet go off to iDisk, which is something I do every hour or so when I'm working on an important document.

The online backup service I like the best is Amazon S3. Amazon has designed it to be extremely reliable and available, it's widely supported, and it's very cheap. For example, .Mac costs about $6 per GB per month, but S3 is only 15 cents per GB per month, or 13 times cheaper. S3 also charges a transfer fee of 10 cents per GB in, and a bit more coming out; transfer in is what you'd use for backup. If you transfer 50 GB a month, which is a huge amount to transfer online, that's still only $60 per year. (At DSL speeds it would take about a week to transfer 50GB, assuming the line is doing nothing else and your computer stays up for a week.)

Also, as far as I know, .Mac works only with OS X, whereas S3 works with any system, so you can use it to share files across platforms.

I use S3 in three ways:

• I use Jungle Disk (available for Windows, OS X, and Linux) to create an S3 virtual drive, and then use the Mac Finder to copy files to that drive.
• I use Jungle Disk's built-in backup program. I just started this, so don't have any results to report yet.
• I use a Transmit droplet to copy files to S3 while I work.

There are numerous online backup systems for Windows, but probably none are as cheap as S3.

As I've said, S3, or any online storage, is really convenient for small files. For large amounts of data, it's still a good long-term solution, but it takes a lot of time to upload the data. It's worth it, however, for important data that doesn't change. I have thousands of photos on S3 that are now backed up by Amazon in addition to the backup I keep myself (hard drives and DVDs). But it was very troublesome to get them uploaded. Uploads I start generally freeze or quit after about a day. Then I have to see what got transferred and start another upload. It's taken weeks, with many stops and starts, to get the photos uploaded, and I have many gigabytes of new photos that aren't yet uploaded. An ongoing project. It's possible that Jungle Disk's built-in backup utility would do a better job, but I haven't tested it yet for my photo data.

Dealing With the Threats

So far I've discussed backup principles (independence being the most important), the six threats, and described hardware and software choices. Now I'll discuss more specifically how each of the threats can be dealt with. To make things a bit simpler, I'll group the six threats into three major categories, because several backup methods deal with more than one threat:

1. User Error, Computer Failure, and Disappearance
2. Surge
3. Office Destruction and Regional Disaster

Backup for User Error, Computer Failure, and Disappearance

For desktops that stay connected to lots of things anyway (network, speakers, keyboard, mouse, external drives, iPods), you should attach a large external drive, via FireWire or USB 2.0, and keep it running all the time. If you turn it off you'll forget to turn it on again and you'll miss backups. You don't have to worry about surge or fire, because they're in a different threat category (see below).

One of the best things about keeping an external drive permanently connected and switched on is that backup to it can be completely automatic. For that to work, the backup software has to run automatically as well. Of course, your computer has to be on for the automatic backup to run, which generally means leaving it on all the time.

For a laptop, you'll have to connect it when you want to back it up and then disconnect it. Backups won't be entirely automatic.

If all your data is on your computer's internal disk, it's best to get an external drive that's the same size or bigger and just copy your entire disk to it each night, or, if your have a Mac running OS X 10.5 (Leopard), use Time Machine, which does copy all the data to the drive, but in the form of versions. (It's straightforward but slow to recreate a crashed internal disk from Time Machine. You boot from the Leopard DVD. Here's an article about how to do it.)

If you have several active disks, there are two cases:

• You can back them up individually with separate backup jobs. This means one backup drive for each active drive, or, perhaps you can fit more than one active drive on a large drive, assuming the backup software allows you to do that.
• Sometimes one or more external drives contains data that changes rarely, such as an image archive. In this case you might back up such drives only occasionally, or even keep several generations of DVDs instead. Peter Krogh recommends in The DAM Book (DAM stands for Digital Asset Management) that you organize your photos into DVD-sized folders he calls buckets, starting a new bucket when the previous one fills up, and then you can easily copy a bucket to a DVD.

On a Mac, if you don't have Leopard you should use Super Duper to clone the internal disk.

On Windows, there are lots of choices for cloning the internal disks, including Complete PC Backup, which comes with Business, Ultimate, and Enterprise editions of Vista. (But see above for its limitations.)

Other choices for backing up your entire Windows system are Norton Ghost, Retrospect, and Acronis True Image none of which I have tested. (I did use Retrospect for years, but never had to do a restore.)

(31-Jan-2008 update) I've now tried Acronis True Image Home ($37 or so from Amazon), and it seems like a fine program that works well. It can image your main drive, so you can boot directly from the backup, and also back up just the folders you want. It's a much better choice than the backups built into Vista (Complete PC Backup and Back Up Files) because it allows you to verify the backup and restore individual files (without installing VHDmount, which is a pain), and, unlike Back Up Files, it allows you to control exactly what's backed up. It can even send you an email when its finished. There's a 15-day free trial.

Most complete system utilities refresh the backup by only replacing files that have changed. But you don't get to keep previous versions; all you have is the most current complete backup. Also, if the backup fails, you may have nothing, which might mean that you are not backed up at all, which is an unacceptable situation, even for a minute. A practical solution to backup failure, since it's pretty rare, is to put in into the Office Destruction category, which I will discuss shortly. In other words, if the backup fails and the primary disk also fails, you will suffer the pain of recovering from Office Destruction. If that's too much, then take the external backup drive offline once a week (or every other day, or whatever) and replace it with a fresh one, perhaps rotating the drives so you don't have to keep buying new ones.

Backup for Surge

A surge protector is a good idea, but you still have to protect against surge, and that requires that the backup device be completely unplugged. The drive you're using for automatic backup (protection against User Error, Computer Failure, and Disappearance) can't be unplugged, so it doesn't qualify.

If surge is very common in your area (either from power-utility problems or from lightning), you may want to keep a weekly complete backup drive offline, just as you would to protect against both the nightly automatic backup and the main computer failing simultaneously. But, if surge is rare, and especially if you're using a surge protector, you can simply consider surge to be Office Destruction and deal with it that way (next section).

Backup for Office Destruction and Regional Disaster

To protect against these attacks you have to get the backup media offsite, and there are only two ways to do that:

1. Physically move it offsite, by walking it, driving it, or sending it somewhere else. (Walking it probably won't get it far enough away to protect against Regional Disaster.)
2. Store the backup online, making sure the online site is very far away. (If you live in a large city you might find out it's in your building. Check that out!)

Both options have severe disadvantages, which is why you can't use them for your nightly automatic backup. Fortunately, both of these severe forms of attack are very rare, so you may be able to afford much longer restore times than you would when recovering from, say, Computer Failure, which is very common. You're going to need the longer time anyway, because you might have to drive across town (in flood waters maybe) to retrieve your backup drive.

The actual backup hardware and software for offsite backup isn't any different from what you use to protect against User Error, Computer Failure, and Disappearance (see above). The difference is the independence you gain by moving the media or device offsite. The problem is that this requires extra work and isn't automated, so it may not happen. It doesn't do any good if an office fire destroys the drive that's been next to the door waiting for somebody to take it away.

I use two drives: One is offsite (at a friend's house, about 20 miles away), and the other is in my office. About once a week I write a new backup to the drive that's at hand, and then I take it with me when I see my friend and swap drives. That way I have at worst a one-week-old backup 20 miles away. (Of course, a one-hour-old backup is online, hidden underneath my desk, but that's to deal with a different group of threats, as I explained above.)

I'm the least qualified person in the world to give anyone advice on how to develop good organizational habits, but here's some advice anyway. These are things I actually manage to do.

• Designate special drives, at least two, for offsite storage. Don't just use whatever other drives might be available.
• LaCie makes drives that are bright orange, which I like because if I see them on my desk I know they're not where they belong.
• Set up easy-to-use computer procedures, possibly even scripts, to populate the drives so you won't have to hassle with various dialog boxes each time. Most backup utilities let you set up a script.
• Keep the drives in special boxes so you'll know that they have to go. A bare drive is too likely to be mistaken for ordinary office clutter. (My article about this is here.)
• As soon as you've written the drive, put it in its case and then carry it to your car. That way, even if you forget to take the drive anywhere, it's driving around with you instead of sitting in the same room as the computer. (The data on the drive is, of course, encrypted; see above. (8-Feb-2008 update) I'm not encrypting it now. See the blog article for why. )
• After you exchange drives, keep the old one near to the computer so it will be handy when it's time to write it, but in a media safe (see above).

Since you're protecting against very rare events, it's not necessary for the offsite drives to contain a complete system backup. I only backup my own folder tree, skipping the OS, application programs, and general preferences and settings. If my office is destroyed or there's a regional disaster, I'm willing to spend a week rebuilding my system. But I am not willing to lose any irreplaceable data.

For active work, I don't want to risk losing a week of data. I keep a USB flash drive near my computer (even in the PC Card slot on my laptop), and write to it as I work. I burn CDs and DVDs and put them in my media safe, or take them to my friend's house. Remember, as long as the media or device is small and not plugged in, you're protected against User Error, Computer Failure, Disappearance, and Surge.

My Backup Plan

I've mentioned various parts of my own backup plan already, but here's the whole plan organized by form of attack. You should organize your own plan that way, too, to ensure that you're covered.

1. User Error. Occasionally the Windows Recycle Bin or Mac Trash, but mostly by Time Machine, since I do nearly all of my work on OS X. My Vista machine keeps Previous Versions, but so far I've never used them.
2. Computer Failure. I have Time Machine and a bootable complete backup written every night by Super Duper (temporarily suspended until they get Super Duper working on Leopard). In addition, I write files I'm working on frequently to an external hard drive, to a flash drive, to my web hosting site, and to a Transmit droplet that copies them to online S3 backup.

   Various application programs I use, such as BBEdit and Lightroom, also keep their own backups, which they write to an external drive.

3. Surge. My computers and external drives are plugged into a Brick Wall surge protector. Other than that, I consider surge a form of Office Destruction.
4. Disappearance. Loose backup media are kept in several media safes in obscure parts of the house (e.g., a basement shelf hidden by the usual basement junk). My external drives are on a shelf under my desk. (I'm assuming burglars don't read my blog.) I also have a home alarm system, leave the lights and radio on when I'm away, and so on, but I doubt that helps much.

   As I mentioned, when I travel my laptop usually stays connected to my arm or shoulder.

5. Office Destruction and Regional Disaster. I treat these the same, as Regional Disaster. A copy of all my own files (not OS or applications) is written once a week and exchanged with last week's copy which is kept at a friend's house. I sometimes take DVDs there as well.

   Also, my photographs (most of which are on the hard drives also) are backed up onto Amazon S3 and onto DVDs.

Evaluating Your Backup Plan

Maybe you don't have an explicit plan, but let's call whatever you're doing now your plan. You should consider each of the six threats one-by-one and ask yourself two questions about each:

1. If the destructive event occurs to your primary computer, will your backup be destroyed?
2. What would you have to do to restore? Don't forget to consider hardware replacement, too.

If you're currently unprepared for any threats, add backup hardware, software, and procedures to ensure that the threat is covered. You probably can't afford to back up all your data to protect it against the more unusual threats (e.g., regional disaster), but at least the irreplaceable data should be completely protected.

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