Viper 60s Theory Of Operation And Maintenance Manual page 105

VIPER SCSI COMMANDS
The COpy command does not write Filemarks between Segment descriptors. The data
appears as one file on tape if multiple segment descriptors are used.
The Viper drive issues READ or WRITE type commands to the other device, depending on
whether the remote device is the source or destination for the data. Each command has a data
length equivalent to the remote device block size.
The block sizes of Sequential (SEQ) devices are specified in the Segment Descriptors. To
determine the block size of remote D/ A devices, the Viper drive issues a MODE SENSE
command each time a new Segment Descriptor is processed. Viper drives accommodate
devices with a block sizes of 256,512, 1024,2048, and 4096 bytes.
Viper drives use only 512-byte blocks. When the other device has a block size of 256, the
number of blocks to be copied must be an even number, and the Residual is reported in
sectors. The Viper does not disconnect during a data transfer when transferring 256-byte
blocks.
Prior to issuing a WRITE or READ command, the Viper determines the block size of the D/ A
device and the number of blocks to be transferred and converts this to 512 byte block intervals
for the Viper drive to complete the requested transfer correctly.
Bus transfer length relates to the Viper drives selectable buffer disconnect feature. This is
configured by placing jumper clips across pairs of pins in the disconnect size area of the
configuration jumper block. The disconnect size selected must be 16K or greater for the copy
command to work. See Chapter 3, INSTALLATION.
The Initiator issuing the COpy command is responsible for any applicable device reserva-
tions (see RESERVE UNIT command description). Also the Initiator is responsible for posi-
tioning the tape to the starting source/destination positions on sequential devices, and for
insuring that the device which is logically connected to the managing Viper drive is properly
initialized.
The Initiator must support the Disconnect/Reconnect option. If it does not, when the COpy
command is received by the drive,
it
immediately terminates the command and returns
Check Condition and an Illegal REQUEST SENSE Key.
5.19.4 COpy Parameter List Header Block
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