Hi!
Trying to kill the keyboard, [EMAIL PROTECTED] produced:
> A QIC tape has 40+ tracks recorded in serpentine fashion. This means it
> records a track in the forward direction
> then moves the head and records in the reverse direction. So each section of
> tape is rubbed past the head 40 times.
> If you verify then 80 times.
> With 4mm DAT you start at the beginning and write until the end in 1 pass.
> If you verify then 2.
You miss that - while it may be a better idea not to go over the
tape many times if possible - QIC cartridges are build to survive
in their environment (unless you go cheap) and so are DAT tapes.
(Like a heavy truck is designed to carry many times the amount
a car can.)
> If you have a damaged section of tape, (worn or crinkled) then the drive has
> to try to read that section 40 times.
*IF* the tape is full. But if the tape is worn, you should
probably use a new one --- same with DAT. Oh, I hear tell
that some DAT-Drives (used to) tear up tapes for breakfast.
DAT-Tapes (unlike the Travan-QIC format) have to be pulled out of
their protective casing and wound round an intricate mechanism
to be written or read --- causing much more wear than other
casing designs.
> Most QIC tapes are designed with a belt which physically presses against the
> recorded surface of the tape the
> entire time. This belt is also prone to problems. If you open the tape door
> on a cartirdge you can see the
> creases down the middle of the tape from the belt.
Casette recorders use the same method of tape transport (and so
do most tape machines, video recorders, ...). I would wonder if
DAT moved the tape with a constant speed without doing that ...
Oh, did I mention that QIC tapes are designed with these things
in mind?
> DAT tapes cost about $10-12.
> TR4 is $26+.
Check. OTOH, do DAT tapes survive at least half the time QIC's
survive?
> QIC tapes are preformatted. There is a map at the beginning of the tape
> which says, segments x,y,and z are bad
> so don't write there. If new defects develop then they will not be detected
> until you verify the tape.
Similar error conditions can exist with R-A-W. You just detect
a few.
> Verifying requires a separate pass and is often skipped.
Which is true even for DAT tapes. User stupidity is not bound
to a tape format (nor to an OS or anything else).
> So many users don't find out
> about the unreadable tape until
> you need to restore.
see above
> DAT tapes are formatted on the fly as the data is being backed-up. There is
> immediate read-after-write verification
> occuring as the data is written. If it is unreadable then the drive keeps
> rewriting the data until it passes the bad area
> or it gives up (typically after 16 attempts) alerting you to the problem.
R-A-W can only compare with the tape drive's buffer, not with
the HD. You still need to test if you can restore from you
tapes and you still need a verify.
> DAT is more expensive. But you'll save in the long run in the price of the
> cartridges. You will save over $100
> buying 10 tapes. There are plenty of 4mm DAT's for $600.
Depends, again, on the size of those 10 tapes and their average
life time --- and on how much tapes you really need.
So. in short, stop being an alarmist when you point out that DAT
offers something for it's increased price (which may or may not
be worth it to a user).
-Wolfgang
PS: Do DAT's need retensioning? No? Well, QIC's do, and they
are stretch and heat sensitive as well.
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