Data Restoration

Restoration

Many people only think of data backup, but don't consider the equally important process of data restoration. If you don't have a clear idea how you would reconstruct your data from your backups, then you have not finished making your backup plan. The steps and structures we outline in the file management, backup and validation sections of this website show you how to create a backup plan that makes the process more orderly.

Test your restoration before you need it

This is one of the most important components of a backup plan. Some parts of this can be very simple and quick, and some may take a while to perform. For instance, if you have a simple mirror of your archive on a separate drive, restoration tests can be really simple. Use catalog software to check that all files are present and accounted for. If you've been using a validated transfer to create the backup copies, then this should be straightforward. As long as the backup drive is in good shape, you're covered by it.
Read more about Validated Transfers

If you use optical disc as a second backup media type, then you should do some spot-checking for integrity of the media itself. Of course, the ability to do an orderly restoration depends on an orderly relationship of the files on the optical media to the primary version of the data. If you are constantly moving files around in folders, or adding new files to existing folders that have been backed up, you may be creating a disorderly mess. This is why we like an additive backup system.
Read more about validating Optical Media
Read more about Additive Backups

Compressed and incremental backups

Restoration can be a more complicated process if you use some sort of compressed backup plan. A simple compressed backup may only require the equivalent of unzipping in order to be restored. But any backup that does incremental updates will be a much longer process. The computer must sift through all the changes that have occurred to the files since the start of the process, restructuring and reconnecting files. If you use digital tape for your backup, this can be further complicated by the need to rotate tapes in order to gather all the data.

Apple's Time Machine is an example of a compressed backup with incremental changes. While you can "see" which files are backed up, you can't actually get at the files without running some kind of restoration process. We have not found Time Machine to be foolproof, and, in fact, it failed to produce a bootable volume in at least one of our tests. If you are going to depend on Time Machine (or a program like Acronis on PC), you'll want to test the restoration of the drive before you have a catastrophic failure.

If you choose to implement some kind of compressed, incremental archive, we strongly recommend that you go through the restoration process before you need it, in order to certify that the process will work for you.

Boot drive backup restoration

If you are making a copy of a boot drive, it's important to validate that the backup is bootable and whether the backup is compressed or not. This should be done, at the very least, when you put the backup software into service. Make sure that it really produces a bootable copy of your drive that works on your machine.

If you have problems

If you find you need to do a data restoration, you will be, shall we say, on edge. Make sure not to create a cascade of errors. Take a deep breath. Find your center. You want to follow the Hippocratic oath: first, do no harm. Here are some tips:

• Know when you need professional help.
• If files disappear or mysteriously become unreadable, establish whether it’s a virus causing the problem. Check virus protection software for updates. The McAfee or Albion Research websites outline current viruses.
• If a voice in your head says that a drive is acting strangely, believe it and make sure you are backed up. Don’t wait. This is a good time to make or update a second backup of the data. It may be that your primary copy has become corrupted, and in that case, you don't want to inadvertently damage an existing backup.
• If you are using drive utilities to work on a misbehaving drive, make sure you have made good backups before using the utilities.
• Use the newest versions of your drive utilities. If you have an older version, update before running.
• Don’t get impatient and start plugging and unplugging drives or switching them off and on. Sometimes the computer might be working hard in the background to fix the problem, and stopping unexpectedly can make it much worse.
• When you have to restore, buy a fresh drive to restore to. You don’t want to make more problems by mistakenly clearing important files off drives to make room for the recovered files.
• If some files are readable and some aren’t, make sure to back up what you can read.
• When you are finished, test for completeness and file integrity. Don’t do anything with the old drive until you are sure that all the files have been recovered.

Restoration of an archive depends on the catalog

A good comprehensive catalog of your images is essential to successful restoration. Without a catalog, it's nearly impossible to know what is supposed to be there. Of course, this means that you need to make good backups of your catalogs. We suggest that you treat your master catalogs as works-in-progress, even for old work. Keep your catalogs in a place that gets automatic regular backup, as well as periodic offline backup. You might even want to burn them to write-once media periodically for added protection.

Use the catalog to check for completeness

When you restore from backup, a comprehensive catalog can let you know that everything has been recovered. This is invaluable if you are faced with an expensive data recovery scenario for a failed drive. If the drive has been well cataloged, you can know with certainty whether everything has been recovered, or whether you need to spring for costly extreme measures, like clean-room recovery. You can use the catalog to research what's missing as soon as you are aware there is a problem, and to check for the completeness after you've restored from backups. Figure 1 shows the Find Missing Items command in Expression Media.

Figure 1 You can use a catalog to determine what is missing both before and after a restoration. Your catalogs will need to be complete, and they will need to be backed up safely.

Check for data integrity

Once you've recreated the archive to completeness (or as much as is possible), you'll want to confirm that there is no corruption, virus or other problem with the files.

• If you've used a validation program like ImageVerifier, that's the simplest way to check, as long as the files have not been updated since the hash was first created
• For a DNG archive, validation is accomplished by checking the validation hash in the file itself.
• An archive of proprietary raws can be checked for valid structure by running the files through the DNG converter and checking for errors (the resulting DNG files can then be thrown away if you like).
• Once the files have been validated for structure, you could also check them visually, by cataloging the images with an image viewing program that will recreate thumbnails for the pictures. Images with corrupted image data will show with corrupted previews, as shown in Figure 2.

Figure 2 Here is an image with corruption in its image data, but has a valid file structure. The only way to check for corruption in most file types is by visual inspection. DNG files that were created with an embedded validation hash can be checked automatically.