ST(4) BSD/hp300 Kernel Interfaces Manual ST(4)NAMEst — CCS SCSI tape driver
SYNOPSIS
tape st0 at scsi? slave ?
DESCRIPTION
The st driver was written especially to support the Exabyte EXB-8200 8MM
Cartridge Tape Subsystem. It has several extensions specific to the
Exabyte, but should support other tape drives as long has they follow the
ANSI SCSI-I specification. Besides extensive use with an Exabyte, the
driver has been tested with an Archive QIC-24 tape drive. The st tape
interface provides a standard tape drive interface as described in
mtio(4) with the following exceptions:
1. Density is dependent on device type. Current Exabyte hardware has
only one density. The EXB-8500 drive, when released, will have a
high density format of 5.6GB. On an Archive QIC-24 drive the driver
reads both QIC-11 and QIC-24 formats but writes only QIC-24.
2. Only the ``raw'' interface is supported.
Special Exabyte Support:
The MTIOCGET ioctl(2) call on an Exabyte returns this structure:
struct mtget {
short mt_type; /* type of magtape device */
short mt_dsreg; /* sc_flags */
short mt_erreg; /* high 8 bytes error status */
/* low 8 bytes percentage of Rewrites
if writing, ECC errors if reading */
short mt_resid; /* Mbyte until end of tape */
};
Bit 4 in the minor device number is used to select long filemarks or
short filemarks. A long filemark occupies 2.12 MBytes of space on the
tape, while a short filemark occupies 488 KBytes. A long filemark
includes an erase gap while the short filemark does not. The tape can be
positioned on the BOT side of a long filemark allowing data to be
appended with a write operation. Since the short filemark does not con‐
tain an erase gap which would allow writing it is considered to be non-
erasable. If either type of filemark is followed by blank tape, data may
be appended on its EOT side.
Bit 5 in the minor device number selects fixed block mode with a block
size of 1K. Variable length records are the default if bit 5 is not set.
For unit 0 here are the effects of minor device bits 2,3,4,5. For other
units add the unit# to each of the device names.
norewind high short fixed
density filemarks block mode
rst0
nrst0 X
rst8 X
nrst8 X X
rst16 X
nrst16 X X
rst24 X X
nrst24 X X X
rst32 X
nrst32 X X
rst40 X X
nrst40 X X X
rst48 XX
nrst48 X XX
rst56 X XX
nrst56 X X XX
SEE ALSOmt(1), tar(1), mtio(4),
EXB-8200 8MM Cartridge Tape Subsystem Interface User Manual..
BUGS
The HP 98268 SCSI controller hardware can not do odd length DMA trans‐
fers. If odd length DMA I/O is requested the driver will use the "Pro‐
gram Transfer Mode" of the Fujitsu MB87030 chip. Read requests are nor‐
mally even length for which a DMA transfer is used. If, however, the
driver detects that a odd length read has happened (when a even length
was requested) it will issue the EIO error and the last byte of the read
data will be 0x00. Odd length read requests must match the size of the
requested data block on tape.
The following only applies when using long filemarks. Short filemarks can
not be overwritten.
Due to the helical scan and the erase mechanism, there is a writing
limitation on Exabyte drives. “tar r” or “tar u” will not work (“tar
c” is ok). One can only start writing at 1) beginning of tape, 2)
on the end of what was last written, 3) "front" side of a regular
(long) filemark. For example, you have a tape with 3 tar files. If
you want to save the first file, but overwrite the second two files
with new data, on a normal 1/4" or 1/2" drive you would do:
mt fsf 1; tar cf /dev/nrst0 ...
but for an Exabyte you need to do:
mt fsf 1; mt bsf 1; mt weof 1; tar cf /dev/nrst0 ...
The regular long filemark consists of an erased zone 3.8" long
(needed to begin a write). In this case, the first filemark is
rewritten in place, which creates an erased zone after it, clearing
the way to write more on the tape. The erase head is not helical.
One can position a tape to the end of what was last written by read‐
ing until a "BLANK CHECK" error is returned. Writing can be started
at this point. (This applies to both long and short filemarks.) The
tape does not become positioned somewhere down the "erased" area as
does a conventional magtape. One can issue multiple reads at the
"BLANK CHECK" error, but the Exabyte stays positioned at the begin‐
ning of the blank area, ready to accept write commands. File skip
operations do not stop at blank tape and will run into old data or
run to the end of the tape, so you have to be careful not to “mt fsf
too_many”.
Archive support gets confused if asked to moved more filemarks than there
are on the tape.
This man page needs some work. Some of these are not really bugs, just
unavoidable consequences of the hardware.
BSD November 30, 1993 BSD