Too often when someone becomes convinced they need to backup their data the first thing they do is start researching backup software. Wrong -- selecting the software is the last step in the process. First you have to have a plan:
The first step in the process is developing a backup plan. The plan should comprehend:
What do you want your backup to protect you against?
Catastrophic failure of the entire system or at least your hard drive?
This is the scenario that most people think of when they decide they should be "backing up." This is simplest and easiest type of backup.
Loss or damage to individual data files such as financial records or work in process?
This is the type of backup where things start getting interesting. Picture this scenario: you are working on your doctoral disertation or term paper or major project, whatever; at the end of the day you save your work and unbeknown to you the file is saved to a bad data sector and is trashed; then as part of your daily routine you backup by a simple system that either mirrors the data or replaces the changed files on the system; the next day to your horror you discover your project file was trashed file; no problem, you just go to your backup copy and drag the it back to your working drive; but to your even greater horror you find it is also been clobbered. It is then you remember your backup which replaced the good file from day before yesterday with yesterday's damaged file.
Loss of irreplaceable archival information such as the video of your child's birthday party or the family photo album?
This may call for a different solution than the other types of backups.
All of the above?
Ideally you will be able to develop a solution that will handle all of the above but it does raise the bar.
How often will you backup, continually, daily, weekly, monthly, only when you think about it?
Perhaps a better way of asking this question is, "How much of your work are you willing to lose and have to redo when the disaster occurs and you need to recover from the backup?"
How much time are you willing to spend on backups.
The more you backup the longer it takes and you really don't want to be using your system while backups are going on.
How disciplined are you?
Many of us have good intentions about doing backups but as the old saying goes, "there is many a slip twixt lip and cup." In other words good intentions don't get backups done. You either have to be very disciplined or the backups should be automated so you don't have to ever think about them until they are needed.
Perhaps most important of all -- how will you recover from a backup.
Will you always recover the entire system? Will you recover only selected files? Do you want the capability of doing both?This is obviously related to number 1 on the list but it is important because there are utilities that are good at backing up, but not so good at recovering or not so good at recovering from different situations.
Once you have the answers to the questions in the backup plan you have the information needed to choose a backup strategy. There are four common strategies and of course each has its pros and cons.
Clone -- probably the most frequently used backup strategy today. A clone is simply a duplicate image of the entire system.
Pro -- simple to implement, relatively inexpensive baclkup solutions such as SuperDuper and Carbon Copy Cloner available, drag and drop file restore possible, clone can be bootable.
Con -- Cloning can take a long time, even if the clone only replaces the changed files, clones take as much disk space as the original, clone backups subject to overwriting with damaged files.
File synchronization -- This strategy may or may not begin with a clone backup consists of copying only the new and changed files to the backup volume on a regular schedule. Often used to keep a clone up to date.
Pro -- Relatively simple to implement, several inexpensive to free software solutions available, much faster than a full clone, depending on the application chosen the backup can n be compressed saving lots of disk space, if uncompressed drag and drop recovery possible.
Con -- backups subject to overwriting with damaged files, if data compression is used you must have the application installed and running to recover, determining the changed version is usually dependent on date time information in the directory and can be inaccurate.
Evolutive Mirror Backup -- This is similar to the Synchronize backup, with a significant difference. Up to n versions of each changed file is maintained. Older versions usually are often stored in invisible folders but are accesible through the backup index maintained by the backup software.
Pro -- if version n is corrupted, you can go to the n-1 copy or the n-2 etc. you may lose some work, but not everything; backups often compressed to save space.
Con -- software solutions generally more complex and more expensive; recovery, either of a file or the entire system, require the backup application.
Incremental Backup -- Essentially the same as the Evolutive backup except the backup copies are in dated folders and not invisible.
Pro -- Everything that was said about the Evolutive backup plus, if the backup is not compressed, a file can be recovered by drag and drop; it may be easier to recover several files this way, backups may be managed outside of the backup utility.
Con -- software solutions generally more complex and more expensive; recovery, if compressed recovery either of a file or the entire system will require the backup application, if uncompressed this can take a lot of disk space
The choice of backup media is dependent on several factors including cost, speed, ease of use, availability, and type of data to be backed up.
Hard drive -- the fastest and most commonly used today.
Pro - easily the fastest media, relatively inexpensive per Byte of data storage, easy to implement and use, can be bootable, the most universally supported backup media.
Con - as large as some drives are their capacity is still finite, like any hard drive backup drives are subject to failure and the same maintenance routines used on and hard drive must be used on backup hard drives. Hard drives are not recommended for long term archival data storage.
CD/DVD -- Probably the second most commonly used backup media and the preferred option for archival data storage.
Pro - many, perhaps most, systems already have a CD or DVD burner so there is no hardware expense. the media is relatively inexpensive and easily obtainable, because you can always get another blank the capacity is in one sense unlimited, media life is many years longer than any other backup media.
Con - burning CDs or DVDs is comparitively very slow, there may be compatibility issues with different brand media and other drives, few software solutions directly support CD or DVD burning, relatively small backup chunks can create issues with recovery of data scattered across multiple CDs or even DVDs.
Network storage -- usually limited to office applications and supported only by a very few apps. This is a complex topic in itself and beyond the scope of this web page.
Magnetic Tape -- at one time the backup media of choice
Pro - high capacity tapes are ideal for backing up very large hard drive systems, media cost per Byte of data storage capacity is probably the lowest of all possible options.
Con - tape drives have become relatively expensive and hard to find, very few applications support tape backup and they are generally expensive, tape backup or recovery is notoriously slow.
RAID - Once limited to the largest systems recent advances have made RAID available to the advanced home user. For a full discussion of the various RAID levels with the pros and cons of each see the AC&NC web site.
Pro - backup is continous and other than the drivers requires no additional software, once implemented it is virtually invisible to the user.
Con - not all raid levels provide true backup and data recovery capability and those that do tend to be very expensive.
There are any number of different backup solutions available and new ones come out all the time. The bulk of these are relatively simple apps supporting either cloning or what I have termed synchronization. Each of these has its own feature set and I have neither the time nor inclination to keep up with them. But among the most widely used are:
Apple Backup - free with a .Mac membership. Basically a synchornization backup, supports iDisk, hard drive, and CD/DVD media
Carbon Copy Cloner - shareware, $5.00 -- the grandaddy of all OS X cloners
Dantz Retrospect - commercialware, $129 and a lite version is often included with firewire drives. Retrospect pretty much does it all on all media. Some find its interface confusing and hard to use.
Data Backup - commercialware, $59. Supports cloning, evolutive, and incremental backups, plus has extensive and very flexible synchronization capabilities. Uses hard drives and optical drives media.
Super Duper - shareware, $19.95. A strong new contender in the clone category. Does everything that CCC does but has a slicker GUI and a lot more clone options
- Tri-Backup - commercialware, $49. The first really successful backup utility for OS X. Supports cloning, evolutive, and incremental backups, plus has extensive and very flexible synchronization capabilities. Uses hard drives and indirectly, optical media, as well as backing up to attached network drives.
My Personal Preferences:
I use backup solutions that are automated so I don't have to remember to do the backup and the backup can take place late at night when I am not using the computer. This means my computer must run 24x7 and the system cannot sleep.
My backup media is a second internal hard drive, that is 50% larger than the drive I am backing up.
I keep one stripped down barebones installation of OS X, not a clone, with the backup utility of my choice on an external Firewire drive so it is available for emergency data recovery. It is also a handy place to run disk repair utilities from and I can attach it to either my desktop or laptop when it is needed.
I use either an Evolutive backup strategy with 10 versions -- no reason for 10 versions other than it seems a reasonable place to stop
I use data compression on the backups to save disk space.
I keep the latest copies of all application downloads on a third hard drive and periodically burn these to a DVD-RW in case I have to re-install.
I backup my user folder, every night with the exception of any cache folders and my financial data is backed up a second time to a third drive.