Poll; Tape drives

[Lennart Sorensen]

On Thu, Mar 06, 2008 at 09:16:58PM -0500, Julian C. Dunn wrote:
> I have to challenge your assertion that it "isn't reliable enough to 
> justify". Tape will last you decades if it's properly stored. Plus, unlike 
> keeping a pile of disks powered on, there are no operational costs in 
> terms of power, cooling, etc. If you have terabytes (or even petabytes) of 
> data, it is not economical to back up to disks especially if that data is 
> infrequently accessed.

If you have enough data that is almost never looked at, then the cost of
a tape drive can be justified, although I think for most users that
isn't likely.  Those that can justify it can also afford to spend
$100000 on a complete archive management system.

I also don't believe some tape formats can be stored and expected to be
reliable.  DAT/DDS certainly never seemed reliable, only relatively
cheap.

> It's true that virtual tape library technology is becoming very attractive 
> and many companies are implementing it, but ultimately, that data does
> (and ought to) get written to tape.

If there is enough data and some of it really doesn't ever get accessed,
then a tape library does make some sense.

For example:
LTO 800GB tapes seem to run about $125 each.
Tape drive appears to be around $4000 although for an extra $500 you can
make it a 7 tape changer.

If we take the 7 tape changer with 7 tapes we get $5375 for a capacity
of 5600GB, although you need a scsi equiped machine to manage it.

If you were to take say 500GB SATA drives at $100 each, you would need
12 drives or $1200 to match the capacity of the tape changer.  Add to
that a machine to put the disks in and manage them along with say a 12
channel 3ware or areca controller for another $1000 (I think that might
be overestimating the cost of the controller), and you should still
manager to have the total system ready to connect to a network (more
flexible than scsi too) for under $3000.  The latency on access will be
much lower on the disk system, and you could add raid5 or 6 for some
reduncancy in case of media failure for only a few hundred dollars
extra.

Certainly a 7 tape changer is much too small to be economical.  I
suspect until you hit 100 tapes or so, it simply can't compare.  Given
the tapes seem to come to $0.16/GB and the SATA disk is at $0.20/GB, it
will take a LOT of GB of storage to make up for the cost of the tape
drive, tape changer and scsi interface.

--
Len Sorensen
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