> The usual
> procedure uses three sets of backups - One in the drive, one in your
> desk drawer at work, and another in a secure off-site location.
I very strongly recommend more than three backups on one of the long term
rolling schemes. Since recovery is a rare event, no one notices that things
aren't going well until it is too late. It is frequently the case that the
damage is obscure and not discovered for several days or weeks.
Just one horror story (that could have been bad but wasn't):
We had not started using contact files yet. One person had played with it
briefly and created a very large file. More than a month later we touched
the file again and were told it was unusable (we were not in open all file
mode so nothing tried to open it). We could find no usable version on any of
our backups. We restored from the distribution originals. Fortunately no
loss because we did not have any useful data in it.
On the issue of more than three copies:
Last week I brought a copy of the database home to play with testing some
potential changes on a system where I could do no damage to the live system.
(I am in the office only 1 day a week). My zip disk had developed a bad
sector since the last time I used it and the payments file was unusable. You
don't know this until you try to restore it. Trying a restore onto the real
data when you don't need to is very dangerous as you can lose the only good
copy. If you do have to restore to recover something, copy the live data to
somewhere as it may be better than what you restore, e.g. I wound up with a
non-usable system with no payments file - bad file from the zip drive erased
the good file on my disk.
In my experience the reliability of various media is:
Hard disk - 100-1000 times better than anything else
Zip disks moderate
Mag tape unreliable
Floppy disks - don't even think about it.
I have no experience with CD-R or CD-WR yet but am about to install one and
evaluate.
