The single most critical element in any digital workflow has to be a foolproof backup or archiving strategy. Memory cards are fragile beasts, subject to corruption and damage or (in the heat of the moment) to being reformatted when you need a 'clean' card in an emergency.

Part of my job specification at school is to be the Press and Publicity Manager which involves taking dozens of photographs each week of special events, including guest speakers. Most of these are simply unrepeatable occasions - the photographs have to be obtained and then stored in such a way that they can be available at a moment's notice - and hopefully twenty years hence!

Storage methods such as ZIP drives have been ruled out because the capacity is too small. CD blanks are cheap and cheerful and would once have served the purpose, but as I shoot in RAW on a D200 where each shot is around 15Mb, I would only be able to store 50 photographs. More commonly I now find myself shooting on 1Gb or 2Gb cards, so CD archiving is hardly practical any more. Which leaves us something in the DVD recording arena - at the moment the High Density mess is too expensive and uncertain to make any safe bets.

DVD-RAM has always had excellent archiving properties. A White paper (Defect Management Capabilities of Various DVD Technologies, May 2004 sponsored by Hitachi-LG) concluded "only DVD-RAM currently offers comprehensive, drive-based defect management", while the Media Sciences Study sponsored by RAMPRG threw in one extra benefit; "Beyond detecting errors and relocating data to a defect-free area, defect management can also compensate for the gradual degradation of the media that is a normal result of repeated overwrite cycles. This protection, and a unique recording layer .. adds to the longevity of the media which allows over 100,000 overwrite cycles".

Not only does DVD-RAM offer defect management (see sidebar), but it is a true random-access medium similar to a hard disk. Unlike DVD+/-RW, individual files can be deleted without having to reformat the entire medium. It does not require special burning software to make it work (e.g. Nero or UDF packet writing applications), nor does it require finalization to make the disk compatible with other drives. It is read-compatible between Windows XP and Mac OS X operating systems. In all cases the blank DVD-RAM will require formatting before use - under XP this typically takes between 2 and 6 seconds to complete (see below). DVD-RAM blank discs are available in a protective cartridge or without it, and as single or double sided media (4.7Gb or 9.4Gb).

Are there any drawbacks to using DVD-RAM? Yes. In the first place not all burners will write to the discs. On my Mac G5 I'm using a Pioneer 111D drive which costs around £23. My Lenovo 3000 N100 laptop already comes with a GMA-4082N DVD-RAM burner, so there is full cross-platform support.
Secondly, the blanks are quite expensive - around £1.60 for a single sided 4.7Gb unit. (purchased from svp.co.uk = £24.73 for 15 blanks inc VAT and shipping - PC World has them for £9.99 for a five pack). Finally, they are slow (2~3x speed). Data from the hard drive (709Mb) took 14 minutes to write to disc and I'm 99% certain this is down to hardware read after write verification. It can be turned off on some drives, but why risk it?

But for peace of mind as well as data security, I can live with these minor irritations.

Formatting DVD-RAM

This is quite easy under Windows XP: simply right-click the drive icon and select format/quick format. The disc will only be formatted as FAT32.
However, XP has a nasty habit of turning on 'CD recording to this drive' which gets in the way of DVD-RAM. Turn it off by right-clicking on the icon and opt for the properties tab - uncheck the CD recording box.

OS X seems to have lost DVD-RAM native writing - a big mystery since it was there in OS 9! If you use Toast 7.x, you can do a quick erase, then eject the disk. When you re-insert it, OS X will initialize it so that it can be written to. Shame that Windows is light years ahead of Apple when it comes to write-enabled DVD-RAM!

Defect Management - Book 2 defines two methods for replacing defective sectors with a good one. The first is 'Slipping' - a method in which a defective physical sector is replaced by the first good physical sector immediately following the defective sector. Defective sectors are listed in the Primary Defect List which is recorded in the Defect Management Area on the DVD-RAM media during formatting.

Linear Replacement is the second method. This is used when a defective sector is found during read/write operations. A defective sector is replaced with a good one in a separate spare area. This imposes seek and rotational latencies that may cause video drop-outs. Defective sectors replaced are listed in the Secondary Defect List which is recorded in the Defect Management Area on the DVD-RAM media during normal operation.

Use something like Nero InfoTool to determine whether your drive supports Read and Write to DVD-RAM