The key to digital archiving is not media permanence. The key to
digital archiving is replication and maintenance.
I use twin, paired backup external hard drives as well as CD-R and
DVD-R media for backup on important projects. The likelihood that two
hard drives will both fail at the same time is infinitesimal; the
likelihood that CD/DVD media corruption will happen is greater than
that but still small. My workflow schema for digital images runs this
way:
* Original captures are written to backup #1.
* DNG Converter writes reduced size original captures to the working
drive. (Scans are simply copied.)
* edits happen on the working drive, creating .PSD and .JPEG files.
* the working drive is backed up to backup #1, with deletions
archived and written to CD/DVD as well.
* backup #1 is synchronized to backup #2.
- The backup and synchronization copying is performed by automated
scripts so it is very consistent and repeatable.
- Backup #1 is connected and powered almost all the time, Backup #2
is only connected and powered when being written to.
- 30-50% free space is always maintained on the internal (working)
drive.
- When the backups become full, two new backup drives (typically at
double the capacity) are purchased to replace them. Directory
catalogs of the old drives are captured, and their contents are
mirrored onto the new backup pair. The old drives are then wrapped in
antistatic bags and stored as a permanent archive.
- Since 1984, I have experienced exactly one hard drive failure. I've
experienced a greater number of file corruptions on DVD and CD media
(every so often, I do a verification scan of several CDs/DVDs to keep
tabs on thos media). For this reason I consider hard drives to be
more reliable for long term storage. However, I don't consider either
media to be "archival" ... I just keep transitioning the data to
newer storage media as appropriate. Prices on hard drive storage drop
every year, and quality improves.
I've never lost any of my digital photo/image data, the archive/
storage chain is unbroken all the way back to 1983. The sophisticated
schema with paired hard drives above was created two-three years
ago... I transitioned to CDR+hard drive from floppy+hard drive media
in 1995, this schema handles orders of magnitude more data and much
more swiftly. My current archive load is approximately 300 added
image files per week, far higher than it was a decade ago.
Godfrey
