A backup is not really a backup unless you know it can be restored. That means it’s possible to put everything back in order in an orderly and reliable way. Here we present guidelines to help you understand the data restoration process.
Compressed and incremental backups
Boot drive backup restoration
If you have problems
Restoration of a photo archive depends on the catalog
Use the catalog to check for completeness
Check for data integrity
Restoration of a video archive depends on the project file
Use the project file to check for completeness
Relinking video assets
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.
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, or renaming files, then you may be creating a disorderly mess. This is why we like an additive backup system.
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 may require 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. Do not feel comfortable that the backup is safe unless you’ve throughly tested it.
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. We do not recommend applying any compression to a boot drive backup.
If you are making a bootable clone, we recommend that you attempt to boot your system from the cloned drive immediately after your first backup. Then launch some of the primary applications you work with and ensure that they behave in an expected way. Do not perform any work that you intend to save, just test that core applications and data properly connect. 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 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 your only 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.
|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.|
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 that creates checksums, use this to verify the data integrity. This can work as long as the files have not been updated since the checksum 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.|
The most recent project file is essential to successful restore a video project. Footage without instructions is good, but does not ensure a complete project. Without the instructions on which footage was used and how to assemble it you just have a lot of data and not a finished video.
Of course, this means that you need to make good backups of your project files as well. We suggest that you treat your project files as works-in-progress, even for old work. Keep your project files 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.
When you restore from backup, a current project file 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. When a project file is opened, it will typically scan all connected drives to ensure that the project assets it expects to use are available.
If files are missing or not in an expected directory, the application will search for the missing media. In this way you can generate a report of which footage is missing. When testing a backup, make sure that the active copy of the data is unmounted and only the backup volume is mounted.
You can use the project file to research what's missing as soon as you are aware there is a problem. In many cases you can perform a restoration from the Virgin downloads that you created at the start of your project.
Video project files typically contain an absolute link to their source media files. If the restored archive uses an identical folder and naming structure, this process may be automatic (just open the project file and look for warnings).
If you’ve needed to rebuild a project archive or have moved elements during the restoration process, you will likely need to relink. All video editing software will allow you to identify a drive or location to search for offline media. Once the application detects footage, it will attempt to load other missing elements contained in the same directory.