In a message dated: Tue, 27 Feb 2001 22:23:41 EST
Benjamin Scott said:
> Travan TR5 is an ideal solution for the small business with between 10 and
>30 GB of data to backup. Drives are cheap, tapes are cheap, and it is easy to
>use. However, they are slow to write, slower to read, and agonizingly slow to
>search. I've also noticed Travan drives and tapes tend to fail significantly
>more often than more expensive alternatives like DDS and DLT, in my personal
>experience.
As I stated previously, I know next to nothing about Travan. I have always
equated Travan with "PC" servers, i.e. an NT or Windows box of some kind.
As a result, I've always considered Travan the drive to use if you really
aren't serious about doing backups, but just want the warm fuzzy of going
through the motions :)
The reason for this is every place I've ever seen using Travan drives for some
reason only has 1 tape, and they use it daily until it breaks or it gets lost.
One site actually had 5 tapes they rotated through. How they got that
scheme to work without actually removing the cellophane from the around each
tape, and removing the tape from the case I'll never know. But they
adamantly insisted that they had a backup solution :)
>On Tue, 27 Feb 2001, Paul Lussier wrote:
>> However, they last, and can be re-written to greater than 10 times each.
>
> *Ten times*? Please tell me that is a typo. I get better reliability than
>that from floppy disks! :-)
10 being the maximum recommended *write* to times. Number of actual passes
I'm not sure about, but a pass is considered anytime the drive head passes
over any section of the tape. Pop a tape into the drive you automatically
have 1 pass. Write to it, you need to rewind, then write, then rewind again
to eject. That's at minimum 2 passes, assuming the tape was at the beginning
for the initial rewind before the write. Need to restore, another minimum of
2 passes. Passes can add up *very* quickly!
Writing to a tape 10 times is quite a lot when you think about the amount of
wear and tear that occurs within the drive and the tape. I would be skeptical
of the data integrity of a tape used more than 10 times. I don't consider the
cost that bad either. I maintain a set of 17 tapes for daily incremental
backups which run Mon-Sat. So that gives me 2 weeks worth of incrementals
on hand at any given time plus a few extra in case I lose a tape for whatever
reason (spilled coffee, bad tape, sudden need for a long streamer ;)
So: 17 tapes x 10 writes each = 170 writes
170 writes / 6 days = 28 weeks
17 tapes x $65 each = $1,105
$1,105 / 170 = $6.50 per write
So, is your data worth $6.50 per day? Sure, you could get it down to less.
Cut that in half by using each tape 20 times instead, and your recurring cost
is down to $3.25. However, what happens if the tape begins to wear out at the
beginning, just after the leader because of so much usage? At that point,
you've lost your volume metadata and restoring is going to be a real pain.
Not impossible, but tough enough that you'll wish you'd only used that tape
a few times less.
Sure, floppy disks can be used more, but there's a whole lot less wear and
tear on a floppy disk than on a tape. You not comparing apples to apples
there. Sure, they're both removable media, but in that case, then why not
just jump to saying that you've got an 80GB removable hard drive that
you can use indefinitely?
>> I don't know the lifespan of Travan or DAT tapes.
>
> DDS and Travan tapes are usually rated in "passes", i.e., passes over the
>read/write head. (Actually, I think DLT tapes are, too.) 2000 is the number
>I usually see. If you verify your backups, that will at least double the
>number of passes. Appending to the end of a tape may also increase usage, if
>your backup solution rewinds at the end of the job, and later searches for
>end-of-data on the next job. The typical worst-case I hear is six passes per
>backup session.
DLT are rated in passes as well, which is why I said I use the tapes only 10
times to write to. If you assume a worst case scenario of 6 passes per backup
session, that's 60 passes right there. If you double my usage numbers to 20
writes per tape, you're at 120. Now, how many passes per restore session?
What about if you randomly yank tapes for verification audits? It's too
hard to keep track of the number of passes. Especially if you have more than
one person dealing with backups, restores, and audits. It's a lot easier
to keep track of the number of writes, you just make a check mark on the
label. Anyone performing backups adds a check to the label immediately after
a write. You get to 10, change the label, I mean the tape ;)
> Be aware that Travan tapes are tracked; as you read through the tape, it
>will wind back and forth from one spool to the other. This increases passes.
As with DLT.
--
Seeya,
Paul
----
It may look like I'm just sitting here doing nothing,
but I'm really actively waiting for all my problems to go away.
If you're not having fun, you're not doing it right!
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