christosz@ppc.ubc.CDN ("Christos C. Z.") (08/05/87)
The following is our opinion and comments on a just installed System
Industries 9625 100 ips tape drive running off a microvax II (VMS V4.5).
If you are interested read on. The drive is an STC (Storage Tech Corp)
drive and SI sells it with an STC interface and an AVIV Q-bus quad
controller (TS11/TSVO5 emulation).
1) The drive (mechanically) behaves just fine without any major problem.
It's an auto-load, caching (256KB), streaming drive with capstan and
tensor arms. Sometimes (1 out of 10) fails to thread correctly
the tape through its mechanism but that's not a big problem.
It has a nice control panel. But you CANNOT select the density
(1600/6250) through software (i.e. BACKUP/DENSITY=...) You have to
do it from the front panel. It's not the drive's fault but the
VMS TSDRIVER.EXE does not support such thing. (There is a rough solution
to that, according to SI, if you map, from the AVIV controller, the
physical drive to two logical drives each with different densities,
e.g. MSA0:, MSB0:)
2) I found out (while doing backups and copies) that in 6250 density mode
there is NO WAY to make it stream. On a microvax (VMS) the actual tape
speed you get is 10-15ips (!), it looks like start/stop and the data
transfer rate is approx. 62.5KB/sec (way out of the average 400KB/s
they advertise). But this is not the drive's fault but the limitation
comes from VMS and the CPU overhead.
(The above figures are in accordance also with DIGITAL REVIEW's tests
on a FUJITSU 2444 100ips drive (they found approx 57KB/sec rate) done
few months ago.)
In 1600 bpi mode the tape really streams fast and it's only there that
you can identify the drive as a streamer. The tape continously streams
without stopping.
3) The spead is slower when you READ from the tape than when you WRITE.
(I think that's common to most drives.)
So what you finally get is a tape drive with approx twice the performance
of the TK50 tape cartridge drive. (And I think this might be always true with
all the other medium-performance tape drives on a microvax.)
Regards, Christos
Pulp and Paper Centre
U. of British Columbia
Vancouver, BC, V6T-1W5
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