We offer data backup as part of our repair services here at Small Dog, as well as data recovery. One question I am occasionally asked is, “what’s the difference?”
Data backup is the process of copying your data to an external storage location, be it a flash drive, external hard drive or a network volume. Typically this is (or should be) done on a regular basis in case something happens to your system. When you check your system in for repair, we always ask if you want us to do a data backup for you, especially if there is a chance that your data could be affected by the repair. If we have to replace your hard drive, your data is not automatically copied to the new drive unless you request it.
In order to copy a file, the system looks at the directory area of the file system. It scans the list of files, locates the one needed, and then retrieves it from the hard drive. If this directory area somehow gets corrupted, it makes copying files difficult. In some cases we can run a repair utility on the drive to rebuild this file catalog.
If the drive is badly damaged due to bad spots on the hard drive platters, a rebuild may not be possible. Data backup looks to the file system to accurately report the location of each file, but if the file system is unreliable, then your backup will fail with an error that it can’t read the files.
When this happens, we have to attempt data recovery. This involves connecting the drive to our server and running a process that bypasses the file system and looks directly at the file storage area of the hard drive. It scans the hard disk for any files that may have become lost, and then attempts to copy them to a safe location. If the hard disk has developed bad areas, this process can take a while. A standard copy operation via Finder will try maybe two or three times to read the file, and then it will give up with an error. (It’s designed to give up before too much time passes so the OS does not appear “hung.”)
A data recovery program is designed to try many more times than the OS normally would, which is why we tell customers that a recovery attempt can often take several days. Depending on how much data there is to recover and how badly damaged the hard disk is, it can take several minutes to recover just one file.
Unfortunately there are no guarantees—data recovery is not always possible. If the drive was physically damaged, such as in a drop, then the attempt might not even recognize the drive. At that point, the only option is to send the drive to a company that specializes in data recovery. They have a clean room environment where they are able to disassemble the hard drive, remove the storage platters, and try to get to the data that way (bypassing the drive electronics entirely.) This advanced forensics does come at a cost, sometimes in upwards of $1000 per drive. Even then, there is no guarantee that you will get your data back.
This is the part where we tell you the best way to prevent this scenario from happening to you is by keeping regular backups. Setting up Time Machine is one of the easiest ways—plug in an external drive, tell Time Machine to use it as a backup drive, and let it do the rest. If anything ever happens to your hard disk, you can just restore from Time Machine. There are also online backup options, such as synchronizing your data via MobileMe.