snip
If you RTFM for the product you'll find that the manufacturer
specifically says NOT INTENDED FOR COMPUTER MEDIA. That would be a
clue.
A house is not particularly good for humidity unless an expensive
humidy control system is installed and used. You'd know if you had one
by the electric bill. Unless you use year-round HVAC there is too much
temp variation.
A bank safe deposit box is good. Bank vaults have a controlled
environment.
Backups to be effective have to have a proper rotation between (at
least) father, son and grandfather, with at least an element of off-site
storage.
Backups have to be done regularly and restores tested on a regular
basis.
How much you spend depends upon what it would cost you if you lost your
data.
I know of one company that did the risk assessment and found that it
would be out of business immediately if it lost its data. Spent a lot
of money on a large (you could have hidden the IT department staff
inside the safe) fire proof safe designed for data storage, with a
large margin of for the period of fire and water that it had to survive.
This was in the days of EDS disks, you know, 11 large dinner plate
platters mounted on a spindle and when removed encased in a clear
plastic cover. The Honeywell system did not provide for tape storage,
EDS would be fine even for back up.
One assumes that the safe and disks survived the fire and the fireman's
water, but they did not survive the descent from the 5th floor IT suite
to the lower basement, nor did the disks.
I have heard rumours, but it could be an urban myth, that some companies
had their IT sites and their off site storage in each of the twin
towers.
The lesson is to run a proper rotation of back-ups, do it frequently and
rotate the media between off-site and on-site. Your off-site store
should be far enough away that a single event will not wipe out your
site and the off-line site. The off-site must not be so far away as to
discourage the regular rotation. You may therefore be able to come to
an agreement with a friend who lives reasonable close by that you
provide off-site storage for each other.
Then you may not need to keep the back-ups in a fire proof safe. You
may need to keep them secure if the data, is sensitive or would be
valuable to some person of evil intent if they got hold of the data.