What is Backup All About?
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, most 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
For photographers, there are three places where your data (images, mostly) are threatened:
In all three places, there are only six types of threats that can destroy data:
- In the camera
- In the field, during or just after a shoot
- Back in the office
- User Error. A user mistake that accidentally deletes or overwrites one or more files.
Examples are reformatting a card by mistake,
losing a card,
and accidentally deleting a folder of images on your computer.
- Equipment Failure. This includes any failure of hardware or software that results in data loss.
We 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.)
Camera and card failures go in this category as well.
- 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.
- Disappearance. This includes burglary, robbery, theft, and accidental loss (leaving a laptop in a taxi, losing a card).
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 camera probably won't take the card in your pocket.
- 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.
- 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.
Of course, not all threats affect all locations equally.
In the field, surge is seldom a problem,
because you're not normally plugged in (it is if you are, however).
In the camera, card failure is a serious threat because most cameras only record one copy of the image;
once you're back in the office and have made a couple of backups, the card doesn't even matter anymore (in fact, it will soon be reformatted).
The Perfect Backup Solution
The almost-perfect solution in the office is to back up your computer every hour to an ultra-reliable, redundant, online storage service such as Amazon's S3.
We 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, we forgot... the photographer needs two T1 lines, because we were going to use two independent services.
Worse, when you're in the field, there's usually no internet access and, even if there were, it would be much slower than T1.
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.
A backup plan therefore consists of a collection of overlapping imperfect solutions, as we will explain in future sections.
And, because digital photography technology evolves and as your use of it changes,
backup is a construction project (see photo at top).