Specifications

I
Intermixing Read and Write Operations on a
No-rewind Tape Device
Many SCSI cartridge tape drives do not support intermixing read
and write operations on a no-rewind tape device. The QIC-02
standard requires this restriction on appending data. SCSI
cartridge tape drives made by Wangtek, Archive, and Tecmar have
this restriction. Certain versions of the Cipher SCSI cartridge tape
drive and some nine-track SCSI tape drives do not have this
restriction.
On a no-rewind SCSI tape device with this restriction, there are
three states of the SCSI tape drive:
❏ A READ state when the tape is being read
❏ A WRITE state when the tape is being written
❏ A GENERAL state.
The tape cannot be read when the tape drive is in the WRITE state,
and it cannot be written to when the tape drive is in the READ
state. The only way to go from the READ state to the WRITE state
is by passing through the GENERAL state. There are four ways to
enter the GENERAL state:
❏ Completion of diagnostics (you power-cycle the tape drive for
a hard reset)
❏ Completion of rewind, erase, or load commands (you rewind
the tape to the beginning)
❏ Attempting to read past the last block of the tape (you create
an end-of-tape, EOT, condition)
❏ Occurrence of an error reading the tape when in READ or
WRITE state.
The last way to enter the GENERAL state, the occurrence of a read
error, is the easiest way to pass between the READ and WRITE
states. By creating a read error to enter the GENERAL state, you
can work around the restriction on writing data to your tape
directly after you have read data from your tape.
7-12 Installing Software Drivers for UNIX