> I apologize for re-opening this thread....but I am trying to
> put together a back-up strategy for a small (6 station) peer
> to peer windows network

> 1. HDD's seem most logical to me - lowest cost per Gig, fast
> read and write cycles. Swappable drives in arrays such as RAID
> seem to make even more sense - pull the drive, put in a fire
> box and insert the alternate drive.  Yet these seem to be less
> available and the cost seems the same as it was 5 yrs ago -
> indicating that this is less than popular.

It's very popular -- for larger servers.  They are much less
cost sensitive than desktop PCs because the reliability needs
are _much_ higher.  And when you are dealing in terabytes of
data the overall system design outweighs costs of single drives.

Personally, I would be concerned about connector system wear if
a spare drives were being removed & inserted on a daily basis.
I don't think that the RAID disk chassis were built for this
many drive exchanges.


> 2. Tape must be less reliable and is definitely slower. Plus
> there is the added cost of consumables.  I am finding that many
> large networks are backed up on tape - perhaps because the
> economics of buying many tapes is better than buying many hard
> drives. Many small networks are backed up on tape, and there are
> still many offerings in this area.

Tape offers compact, robust, stable, removable storage.  Due
to historical incremental development, there is software to
support the concept of off-site backup on to this media.


> Is there a technical reason that tape is still so widely used,
> and am I missing something?

It's reasonably inexpensive and known stable for commercial
time scales (5-10 years) when stored unattended.

This may change because low cost disk drives are now in the
same cost per gigabyte of tape cartridges.  But they will be
more fragile and reliability after multi-year storage is an
unknown (assuming the RAID array still exists).  Products to
automate disk drive swapping don't exist yet -- automated
tape libraries do.

Tape drives have always offered backwards compatability.  In
part to allow reading archival tapes that were written on prior
generation tape drives.

And don't discount social inertia -- since tape has been used
in the past, people will continue to use it.  Managers of large
enterprises aren't real happy with ripping everything out and
changing things all at once; even if the technology is better.

On the product side, you can get automated tape libraries that
have several tape drives and dozens to hundreds of tapes with
a robot to load & unload the tape drives.  They are expensive,
but not nearly as pricey as a human operators on 24x7 service.
With the appropriate software, the cost of the library can be
shared over many servers backing up dozens to hundreds of disks.


> What really is the medium of choice for back-up?

I think a layered approach.  Details depend on a trade-off
between cost and vulnerability.  Like insurance -- the less
risk you assume, the more it's going to cost you.

RAID arrays protect against single device failure for short
periods of time.  But they store only a single snap-shot of
the users' data.  If a user corrupts a file, its content is
lost.  There is no "yesterday's version".  And they are on-site
and suseptible to catastrophic failure (fire, flood, earthquake,
etc).

Tape backups, by using simple rotation and extraction scheme,
are easy to generate a multi-copy off-site library (every day
for a couple weeks, every Friday for a couple months, every
month-end for several years, and year-end forever).  This can
meet the legal requirements for a business to keep financial
and other required records for specified retention periods.

If the amount of data is low enough, CD-R or CD-RW (now) and
DVD-R or DVD-RW (future) may become cost effective, viable
options for backup.

                                                Lee

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