>jkunz_at_unixag-kl.fh-kl.de wrote:
> >On 9 Dec, Gunther Schadow wrote:
> >> Only trouble is, I only have one, suspect, TK70 tape.
> > You can use TK50 tape as well. Just put them under a bulk-eraser
> > first. It is said that the media is actually physically the same,
> > just different labels.
> AFAIK the media is different. Bulk erased TK50 tapes will work like
> TK70, but they will be (probably) not reliable.
> tschuess, Jochen
> Homepage: http://www.unixag-kl.fh-kl.de/~jkunz
Jerome Fine replies:
Memorex used to have a web site that listed all the properties of
DECTape (i.e. I for the TK50 with the name in brown) on the plastic
holder and DECTape II (II i.e. for the TK70). The actual magnetic
and physical properties for the tape were identical. The only difference
that I could ever see between a DECTape and a DECTape II was that
the name for the first was in BROWN and the name for the second
was in BLUE. Now, there must be a very fancy colour recognition
detector on the TK70 tape drive since I understand that after DECTape
is used on a TK50, I have seen the TK70 tape drive automatically
place the drive in WRITE PROTECT mode ASAP.
Now I know that a bulk erase does confuse the TK70 over this
aspect and that blank tapes which have never been in a TK50 are
also OK in the TK70.
(I won't belabour the point. Yes, I realize that the TK50 does write
a tracking code of some kind on the tape which the TK70 is
programmed to NOT overwrite. Typical DEC behaviour.)
I have used the TK50 tapes (after a bulk erase) in a TK70 for several
years now and have had no additional problems related the using a
DECTape instead of a DECTape II in the TK70 tape drive. By the
way, the two advantages of the TK70 is that:
(a) It allows the tape to hold up to 4 times as must data. In my case,
I can get 8.75 RT-11 partitions on a TK70 tape (I actually write
only 8 full partitions) of 32 MBytes each using BUP in RT-11 (block
size of 8192 bytes). Can anyone reading this suggest if going to a
larger blocking factor might get me up to 9 full partitions?
(b) The controller must have a buffer of some kind which holds the
next block of data automatically. When I do a "/VERIFY:ONLY"
operation in BUP under RT-11, the total time to process one
partition of 32 MBytes is about 7.5 minutes - which is also about
the same time to write that same 32 MBytes. I suspect that due
to streaming considerations, the firmware on the TK70 keeps
accepting data from at least the next record of data on the tape
while the CPU is comparing the last n records from the hard
disk drive. If the CPU then commands the controller to issue
a request for the next record of data within a reasonable window
of opportunity (not sure how long that might be - maybe even more
than one record - I know if I was writing the firmware I would fill
all the buffers that were available after doing double that number of
sequential reads), then the streaming mode is not lost and the tape
is kept in motion continually. Contrast this with about 19 minutes
to write a partition on the TK50 and over a hour (I gave up before
even one was complete) with a "/VERIFY:ONLY" operation.
So I really do disagree that they DECTape II is any different
from the DECTape except for the BLUE and BROWN labels -
unless you consider the price that DEC charged to also be a
difference.
Sincerely yours,
Jerome Fine
Received on Sun Dec 09 2001 - 17:13:06 GMT