Storage Issues

Vincent Bockaert,

If you value your digital images, you should have a proper backup system in place. In this article, we will discuss storage issues with Magnetic Storage and Optical Storage (discussed in separate glossary entries) and some backup tips so that you can enjoy your images not only in the short term, but also much further into the future.

Data Stability

Just like magnets become weaker over time, the magnetic properties of a hard disk will diminish in the very long term and can be affected by environmental factors such as strong magnetic fields. The materials which are used to make CDs and DVDs decay over time and the problem is that even minor changes in the data can make the whole disk unreadable. Different brands and different grades of optical media advertise different life spans. It also depends on how they are stored, how well you take care of them, how often they are read, etc.

But regardless of the above lifetime issues, even a simple scratch can render your CD or DVD unreadable. Hard disks are high precision mechanical devices spinning at high speeds, typically 7,200 rpm. So there is always the possibility of failure due to a shock or a power surge. But even without a physical failure, it is possible that you suddenly lose the content of your whole hard disk, e.g. due to corruption of the file structure. So it is important to have multiple backups because data recovery is tricky, as explained below.

Data Recovery

Once a CD or DVD is damaged or corrupted, it is very unlikely that you will be able to recover anything. Chances of data recovery from hard disks are usually very good, but by no means guaranteed. Also, data recovery can be time consuming and expensive. So if you store your images on a hard disk, you should have at least one extra copy on another independent hard disk or on a CD/DVD. By "independent" hard disk I mean an external hard disk which is only connected to your computer when you do the backup. Two internal hard disks provide insufficient protection because both can be affected in case of damage due to lightning or loss of data due to a virus attack. Also avoid storing images in the root directory of a partition as that significantly lowers chances of data recovery via software.

Data Removal

Sometimes you may have the opposite problem: getting rid of your images permanently, e.g. destroy old backups or cleanup up your hard disk before you sell your computer. CDs or DVDs are easy to destroy, but securely erasing data from your hard disk is not as straightforward as it seems. There are plenty of affordable recovery programs which can recover data from a formatted hard disk. Formatting the hard disk, then copying dummy data to the hard disk until full capacity, followed by a format will prevent software based data recovery and should be sufficient for most of us[1].

Long Term Storage: "Migrate, Consolidate, and Refresh"

If we think in terms of decades instead of years, certain media will become useless in terms of capacity, or incompatible, or both. A typical example is the floppy disk which can barely store a single 2 megapixel JPEG image and few computers still come with a floppy drive.

In the nineties, I used 80 MB "magneto-optical" disks [2]. My magneto-optical drive only had drivers up to Windows 98, so I recently migrated these onto my hard disk via an older computer which still had a parallel port and Windows 98.

Some of the CDs burned with older burners are no longer recognized by newer drives.

So to avoid compatibility issues, it is advisable to migrate your data to newer media. Since capacities of magnetic and optical storage are constantly increasing, you can at the same time consolidate your data. For instance, 500 floppies can be consolidated into a single CD, 58 magneto-optical 80 MB disks can be consolidated into a single DVD, 275 CDs can fit on a single 200 GB hard disk, etc. So once or twice a decade you will have to migrate and consolidate your old and small capacity media to the new and larger magnetic or optical media that become available. This has the additional benefit of "refreshing" your data to overcome the earlier mentioned issue of long term data stability.

Backup Tips

  1. Always maintain at least two independent copies of your images, for instance:
    • - one magnetic and one optical (recommended)
    • - two magnetic (e.g. internal and external (disconnected) hard disk)
    • - two optical
  2. To have even more peace of mind, consider:
    • - two independent magnetic backups and one optical backup, or
    • - one magnetic and two optical backups
  3. As a protection against unfortunate incidents such as fire, tornados, floods, etc., store one of your backups in a different location.
  4. Be careful with multi-session CDs or DVDs and make sure you verify the data.
  5. When buying a new system, "migrate and consolidate" your data to new and larger capacity media. This will at the same time "refresh" your data.

Technical Footnotes

  1. (1) Advanced note: (expensive) hardware based recovery techniques used in forensics and intelligence agencies can reconstruct the overwritten data based on physical differences between areas which have been "zero" for a long time and areas which have been "one" for a long time and which were only recently changed into a "zero" via overwriting and erasing. More sophisticated erasing programs with multiple and random write-and-erase cycles will make even hardware based recovery impossible.
  2. (2) They have characteristics of optical and magnetic storage and are very reliable. Currently they come in higher capacities but are less frequently used, rather expensive, and require a dedicated reader/writer.
This article is written by Vincent Bockaert,
author of The 123 of digital imaging Interactive Learning Suite
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