Sunday, May 25, 2008

Backup Strategies for Photographers

Photographers create assets - images. Ideally, these assets can be used for the life of the photographer and beyond.

In the "good" old days of film, the problem was keeping the materials, i.e. negatives and prints, safe from harm (fire, flood, mildew, theft, etc.) and in pristine condition. The latter could be a problem if the materials where not of archival quality or contaminated or whatever.

As "digital" photographers our assets are by nature primarily digital files. The advantage of digital files compared to negatives or prints is that the problems associated with those are easily mitigated or can not occur because of the different nature: keeping a digital file safe from harm is easy is enough copies are kept in enough different physical locations. And deterioration is also not a problem for digital files.

There are, however, a number of risks and issues specific to digital files:

  • All currently available media deteriorate over time.

  • Files may suffer from "bit rot", usually through copying errors or because of media deterioration.

  • Hardware becomes obsolete and it may not be possible to use todays media in 10 or 20 years because the physical connectors are no longer supported, because there are no drivers, or because hardware can not be replaced if it fails.

  • File formats become obsolete and are no longer supported.

Let's look at the specific problems.

Media Deterioration

An old quib is that it is not a question wether a hard drive will crash but when. Hard drives are mechanical devices, so it is just a matter of time until they wear out or dust gets inside or something else goes wrong. And if you think that keeping the hard drive in a cool, dark place will help I have to disappoint you: the lubricants deteriorate and eventually the hard drive will fail. In fact, a drive that is spun up regularly (every few weeks) will last much longer than a drive that is just kept in storage.

Optical media, such as CDs and DVDs will deteriorate quickly if not stored perfectly. And even if they are stored under perfect archival conditions, there is ample evidence that the expected data retention time is much, much lower than the time claimed by manufacturers. A friend of mine, for example, found that after 5 years 20-50% of his burned CDs and DVDs show one or more errors that can not be corrected.

Magneto-Optical (MO) media where guaranteed for 30 years and it seems that these claims where accurate. Unfortunately, this is obsolete technology and the drives are no longer being made.

Ultra density optical (UDO) media are interesting, with manufacturers guaranteeing 50+ years of data retention.The drives start at about USD 1000, media are about USD 2 per GB, so UDO is not cheap. This may still be a viable option if the data is valuable enough.

Solid state memory, i.e. flash, is usually able to retain data for 10 years. After that, all bets are off.

There is, of course, an easy way to deal with these issues: copy to a new medium regularly. Regularly means that you must guarantee that a copy (better: two) is created well before errors can be expected.

Bit Rot

Data may change as the medium it is stored on deteriorates. Data can also change due to copying errors.

There are various techniques to detect and correct bit rot. They all involve checksums and error correction codes to correct problems.

Hardware Obsolecence

Hardware becomes obsolete with time. Do you still have a ZIP drive to read ZIP media? If you do, does it work with your current computer? And what happens when the drive breaks and you need a new one?

It is relatively easy to protect against this if you copy to a new medium (that is going to be supported for a number of years) regularly.

Format Obsolecence

If you have data stored in a proprietary format, chances are that you have experienced this problem already. It seems that every new version of Microsoft Word, for example, seems to introduce subtle differences in the way old documents look.

Data stored in an open format, preferably with one or more open source implementations for reading and writing the format, is much safer from becoming obsolete. It seems that JPEG and TIFF, for example, will be around for a very long time, if not forever.


So how does this translate into a viable strategy for keeping my digital assets safe for a long time?

First off, I keep all my data in open formats. For digital negatives, I use DNG files with XMP metadata. Processed files are stored as TIFF. I must admit that I sometimes also use PSD (Adobe Photoshop), which is proprietary and not open, but only to store working copies, which really only make sense in Photoshop anyways.

I then calculate an MD5 hash over each file which is stored with the file. This way I can easily detect changes to the file.

The files are stored on multiple hard drives. I use a combination of FireWire and USB external drives and internal drives that are quickly swapped using a Sharkoon SATA QuickPort which is a docking bay allowing a SATA drive to be connected to a USB port.

The drives containing multiple copies of the files are stored at home, in the office, and offsite (bank vault, friend's house, etc.).

I have a regular calendar task to check the hashes on every drive every few months. If a single error is found on a drive the entire drive is tossed. This is not a problem as long as there is still a good copy on a different drive. The integrity check has the added benefit of ensuring that the lubricants of the drive get a good workout.

There is another calendar task to replace every drive after it is 3 years old. With the inevitable march of technology increasing the capacity of hard drives, I can consolidate the content of two old drives on a single new drive.


This strategy is probably not perfect, but it does give me a high degree of confidence that the files will still be useable in the distant future.

Canon G9 at 8 MP

A reader has an interesting question regarding the Canon G9 and Konica-Minolta A2 comparison:
If you were to switch G9 to a next-down image size (8MP, no?) would it improve a quality of an image?


Would this work in the same camera (the G9) if you merely changed the settings? Would ISO400 look more like ISO 200? Could ISO 800 be used at all? How does it all compare to A2?

Interesting question!

Wednesday, May 21, 2008

Voltcraft K204 Datalogger on Mac OS X

Conrad Electronic sell the Voltcraft K204 datalogger, which is a 4 channel temperature logger. [Note that the above link is to the German Conrad website. The links to other sites are, unfortunately, not the same, so you will have to perform a search on each national site.]

The logger allows you to capture up to 16,000 samples from up to four different K-Type temperature probes. Depending on the probes, a temperature range of -200°C (-328°F) to 1370°C (2498°F) may be covered with a 0.1°C resolution.

The K204 sports a serial port and comes with a RS232 cable. No Macintosh computer has come with a RS232 port for the last ... what ... decade or so?

Saturday, May 10, 2008

Comparing the 2004 Konica Minolta A2 with the 2007 Canon G9

I have used a Konica-Minolta DiMAGE A2, which was a fairly high-end super-zoom camera in 2004, for about 4 years. In the fall of 2007, I purchased a Canon G9. So how much progress has there been in the last 3+ years?

Thursday, May 8, 2008


Recently I went to India for the first time. What a wonderful place!

I was (and still am) fascinated by the colors, the smells, the bustling business everywhere. The general feel was of vibrant aliveness.

Because my primary objective was not photography, I decided to carry only a Canon G9, not a DSLR. I figured that because of the generally intense sunlight, I would not have to do much high-ISO shooting, so image quality would be acceptable. I also figured that I would deeply regret the shots that I would loose because of this decision.

Well, I was right on both counts. Most pictures were taken in sunlight so bright that sensor density (i.e. the number of f-stops between the highest and lowest levels of light that can be discerned) was the limiting factor, not sensor sensitivity.

And I lost a number of shots because the G9 is so much slower than a DSLR. Try riding in a 3-wheeler cab through dense urban traffic with the driver going like the devil is breathing down his back and then you see an elephant in the fray ... by the time the autofocus had gained focus, we were well and truly on a different street.

I am still rather pleased with the results and in all honesty, since the G9 was just small enough for me to have it with me literally all the time, I probably got some shots that I would not have gotten with a DSLR because the bigger camera would have been in the hotel room or in a bag.

Decide for yourself what you think, there are more images in this gallery!

[caption id="" align="aligncenter" width="640" caption="Boy flying a kite"]Boy Flying a Kite[/caption]

[caption id="" align="aligncenter" width="800" caption="Oxcart delivering ice"]Oxcart[/caption]

[caption id="" align="aligncenter" width="640" caption="Shrine to an unknown deity"]Shrine[/caption]