Poll; Tape drives

[Madison Kelly]

Lennart Sorensen wrote:
> 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.

Off-list I was speaking to a friend who works in IT at a big company, 
and she also voted for tapes, saying that in large scale environments 
"it's the way to go".

It surprises me, in a way. I was expecting to hear grumblings that tape 
was a necessary evil, but apparently it is still a preferred solution in 
larger situations.

As Len mentioned though, up to a (fairly large capacity) point, Disk 
still makes more sense. So then, I need to ask;

Q. What raw storage capacity required is the "break point" where tape 
becomes preferable to disk storage?

If I can answer that, then I can start to decide if people who need that 
capacity are realistically in the range of potential users of my modest 
program.

Thanks as always!

Madi
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