From sharp@noao.edu Wed Oct 27 14:35:55 1999
Date: Wed, 27 Oct 1999 14:35:48 MST
From: Nigel Sharp
Reply-To: sharp@noao.edu
To: jglaspey@noao.edu
CC: ot@noao.edu, em@noao.edu, telsci@noao.edu, sgrandi@noao.edu,
mperalta@noao.edu, sharp@noao.edu
Subject: Exabytes - distribute widely
Exabyte drives and 8mm tape cartridges
The recent taping error on the mountain was due to an incorrect sign
on the lapis drive. rst16 should have said rst24. The signs are also
wrong there for indigo, and at the 0.9m for taupe. There are no signs
at the 4m. For the record, I found the following drives:
lapis, 8505XL, device rst0,8,16,24 where 24=8500 compressed
taupe, 8505XL, device ditto
khaki, 8505, device rst3,11,19,27 where 27=8500 compressed
vanilla, 8505, device rst2,10,18,26 where 26=8500 compressed
indigo, 820, device rst10 (8500) and rst26 (8500 compressed)
pearl, 820, device rst10 (8500) and rst26 (8500 compressed)
There are also 8200 drives in a few places but they don't cause trouble.
I also don't want to pretend this is a comprehensive list (I was rushed).
And for the interested parties, the tutorial follows.
Nigel
----------
Ignoring the Mammoth, aka Exabyte 8900, there are currently two lengths
of tape cartridge, 112 and 160, and four density options, which are 8200
mode, 8200 compressed (aka 8205), 8500 mode and 8500 compressed mode.
Drive identification:
8200 - black faceplate, two vertical lights on left, button on right
8500 - black faceplate, two horizontal lights on left, button on left
8505 - slim format, three lights on left, button is wide, smooth
8505XL - slim format, three lights on left, button is wide with raised dots
8705 - slim format, three lights on left, button is narrow, one bump at top
We have no 8205 drives (which wrote only the first two modes), and no 8500C
drives, which were a large format version of the 8505. The 8500 drive is
still around in a few places, but I didn't see one on the mountain: it can
handle 8200 and 8500 modes, but has no compression.
The 8505 and 8505XL differ only in that the XL drive will take 160 tapes
as well as 112: the 8505 will spit out 160 tapes. These two drives will
read and write all four modes of tape.
The 8705 is also called the Eliant 820 (whoever in marketing chose 820 when
the old drive is an 8200 should be shot).
The 8705 writes only 8500 and 8500 compressed modes: it will read 8200 mode
tapes as long as they are write protected (it spits them out otherwise).
It WILL NOT read 8200 compressed mode tapes (hence the original problem).
Choosing the density:
a) if a tape has been written on, the drive will default to the density
used previously and THERE IS NO WAY TO OVERRULE THIS. To change the
density of a used tape it must be erased using a magnetic bulk eraser.
Most new tapes fresh from the shrink-wrap are erased, but it does seem
that some have been written on (I am guessing, by factory testing).
(Note that Exabyte claim to provide low level commands which will reset
the density, but they seem not to be implemented in Sun's device driver:
if anyone cares to write a new driver ...)
b) using the device name under SunOS. SunOS tapes step by 8, so that device
st0 is the same device as st8, st16 and st24 (similarly for 1,9,17,25, etc.)
The Sun driver implements these in the order 8200 mode, 8500 mode, 8200
compressed, 8500 compressed. Thus, /dev/rst16 on lapis is 8200 compressed
and the label was wrong. Note that the 8705 uses the same driver, so it
only implements steps 2 and 4 (e.g. st8 and st24) for writing. I don't know
what the 8705 does if you write to the other two names: it does something
but I haven't tested the density it uses.
c) using the device name under Solaris. Solaris uses qualifying letters after
the device number, thus /dev/rmt/0 can be 0l, 0m, 0h, 0c and 0u. Yes, there
are five options under Solaris, nominally low, medium, high, compressed and
ultra, except that ultra is not implemented and is the same as compressed.
Solaris decided not to implement 8205 mode, so that l=8200, m=8500 and
h=c=8500 compressed. This makes it harder to write the "bad" 8205 mode,
unless, of course, your tape has already been used at that density.
d) all of the drives sense the density for reading, so you can use any name.
That is, it's the same f you read from rst0 or rst8 or rst16 or rst24,
and under Solaris why type more, just use /dev/rmt/0 etc.