Digital BW, The Print

> From: lenzzman44 [mailto:lenzzman44@...]
>
> I think there might be some confusion here between "back up" and
> "archive". While additional external hard drives are dandy back up, I
> think they are a terrible choice for archiving. For one thing, the
> reason for backing up a hard drive is that hard drives fail! Routinely
> and inevitably. And when it goes, it ALL goes. They are a magnetic
> medium which always deteriorates with time. If they aren't fired up
> periodically, the lubes gunk up.
>    For long term preservation of digital info, the present hands down
> choice, IMstudiedO, is DVD, with its data layer robustly sandwiched in
> plastic. (And then multiple copies stored in geographically remote
> armored hermetic environments<G>, but start with DVDs.)

The optimum backup strategy involves making a new copy of _everything_,
including what was already backed up before, and only deleting the old
backup when the new backup has been successfully written. If during the
backup process you discover that your main copy has become corrupted, and
can't be read, you still have the last backup to copy from. Since you always
have at least two copies, the chances of both being corrupted at the same
time is nil.

With DVDs, it makes sense to copy to a fresh set of DVD-R discs, and then
discard (or demote to backup-backup) the previous ones. But on a hard disk,
this can be done on a file-by-file basis, if you have software that copies
each file to a temporary file, and only renames it over the previous backup
when the copy is complete. Since every backup involves the reading of every
file, not just the new ones or modified ones, you get to find out if your
main disk is going bad before it's too late.

The worst kind of backup is an incremental backup, where you only copy new
or modified files each time onto some optical medium. If one day you
discover that your hard disk is dying, and you pull out some five year old
CD to recover an important file, the chance that the CD is also unreadable
is not insignificant. It's happened to me.

--

Ciao,               Paul D. DeRocco
Paul                mailto:pderocco@...