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Backup for a home computer

May 12, 2012

I just returned from a wonderful holiday in southern Utah, with 297 pictures in my digital camera.  As I transferred these to my computer and began creating a photo album, I could not help but think about backup.  I’ve heard too many horror stories from other people to be complacent about backup.  They say thing like `the hard drive in my laptop died and I lost all my photographs’.  I don’t want that to happen to me.

So, why is backup so important?  All of your valuable documents and photographs are on your home computer.  You may accidentally delete them.  You may modify them, destroying the original in the process.  The disk drive may fail.  Your computer may be stolen.  Your house may burn down.  Your whole neighborhood may be flooded.

To begin, you should determine what you might need to do.  Ask yourself some questions.  Do you want to restore all of your files from backup, restore a single missing file, or recover an original file?  Likely you want all of these.

How valuable are your files or photos?  How would you respond if you lost them?  Perhaps it would be a disaster.  Perhaps you wouldn’t care at all.  Your answer determines how much of an effort you should put into backup.

What risks will you handle?  Some happen occasionally.  Disk drives fail regularly, so you should expect that to happen and plan for it.  Some are quite unlikely.  Your house will likely never burn down.  It’s important to be realistic about risks and their consequences.

How long do you want to keep your computer files?  Will you ever want ten-year-old files?  Will your family ever want them?  Your answer determines how long you should keep backups and what type of backup you need.

There are many options for a suitable backup system.  You may need more than one to satisfy your requirements.  One option is simple redundancy, with two disk drives set up as a mirror in the same computer.  This means that your files will be intact even if one of the drives fails.  Beware that you need to replace the failed disk as soon as possible because you lose the protection once a disk has failed.  You also need to be notified somehow when a disk has failed and once again when the mirror is operational again.  This option does protect against disk failure but provides no protection against deletion or against risks like theft or fire.

Automatic snapshots are another option.  These are essentially periodic backups of changed files on the same disk drive.  Because space is limited, the newest snapshots must replace the oldest ones.  With snapshots, you can revert a filesystem to a previous state or you can restore individual deleted or modified files.  However, snapshots don’t protect against disk failure or risks like thefts or fire.

For more protection, you need to establish a backup rotation system.  This entails taking periodic full and incremental backups.  These are best done on a fixed schedule, one that can be automated.  That way you don’t have to remember to do it yourself.  With such a system, you can restore all of the files from a filesystem or just a few files that are missing or that you modified.  The rotation means that old backups are overwritten with new ones, so that you can only travel back so far in time to restore files.

You can keep the backups on a separate disk in the same computer.  This scheme is convenient but its weakness is that the backup disk can fail, destroying all of your backups.  Offline backups address this problem by using several backup devices that you store separately at the same location.  If one of these fails, you can still recover your files from the others.  You do have to attach or insert one of these devices, generally the one with the oldest backup, to prepare for a new backup.

What if your house does burn down?  Consider offsite backups.  These are the same as offline backups except that you must store the backup devices at a different location.  You may want to keep them at home and also at a relative’s place, for example.  You’d have to work out a scheme to transport the backup devices there and to retrieve them when you needed one.

Finally, we come to archival storage.  This is a way to circumvent the time limit of most backup schemes.  You would use this to preserve valuable files.  Make a complete backup of a set of related files, such as all your pictures from a recent trip.  This is a backup that you never delete, discard, or overwrite.  You will need multiple backup devices, ones that are reliable and secure.  The number of these will inevitably grow.  You should also test these backups occasionally to be sure that the files are still readable.  Depending on the value of your files, you may want multiple copies.  You will also have to transfer them to new types of storage as technology changes.

So far, I have not mentioned what types of devices to use for backup.  There are many options here too, all with advantages and disadvantages.  It used to be that magnetic tape was the medium of choice, but this is no longer the case.  Tape is both expensive and inconvenient.  For home use there are better options.

Writable DVDs are good because of their long life expectancy, assuming that they are treated well.  However, their capacity is only about four gigabytes, making them unsuitable for many backup schemes.  USB flash sticks are better, even though they are more expensive.  They go up to at least 64 gigabytes, and can be rewritten many times.  For even higher capacity, consider removable disks.  They go up to at least 2 terabytes and also can be rewritten many times.  However, any backup device can fail.  It’s better to have many of these to allow for the occasional failure.

Finally, there’s Internet storage for backup.  This is certainly convenient, as long as an Internet connection is available.  The service you get depends on the company that hosts your Internet backups.  Beware that some of these may not guarantee that your files will always be there.  You will likely have to pay to get a service that’s suitable for backup of valuable files.  Consider privacy also.  You may have to encrypt your backup files and keep the encryption key to yourself to ensure this.

As it happens, I’m in the process of designing a backup server for my home computers.  Now that I’m aware of all the options and decisions I have to make, I’m well on the way to accomplishing this.


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