User's Manual

DLT2000 SCSI Interface
8-48 DLT2000/DLT2700 Cartridge Tape Subsystem
Buffered Mode
The drive will implement Immediate Reporting on WRITE commands through
Buffered mode.
If the field is zero, then the drive does not report a GOOD status on WRITE commands
until the data blocks are actually written to tape. If the Buffered Mode field is one, then
the drive reports GOOD status on WRITE commands as soon as the data block has
been transferred to the buffer. This is the default configuration for the drive.
If Buffered mode is not used, the tape drive will suffer a significant degradation in
performance, and maybe capacity as well, depending on tape format, block size and
compression. If writing 2.6 or 6.0 GByte formats, if the block size is a multiple of 4
Kbytes, there is no capacity loss. When using the 10 GByte format, if compression is
disabled and the block size is a multiple of 8 Kbytes, there is no capacity loss.
When using the 10 GByte format and compression enabled, not having buffered mode
enabled will cause some capacity loss, depending on compression ratios. This is
because the block packing feature is essentially disabled by turning off buffered mode.
If this field is greater than 1, the command will be rejected with a Check Condition,
with a Sense Key of ILLEGAL REQUEST.
Speed
The tape drive supports only one speed, the default speed.
Block Descriptor Length
This specifies the length in bytes of all the block descriptors. Since the drive only
allows one block descriptor, this value must be 8 or 0. Any other value causes a
CHECK CONDITION status with an ILLEGAL REQUEST sense key to be returned.
Density Code
This field should match the current density of the media, or will be set to zero if the
density is unknown.
•= 00h - use default density
•= 0Ah - 6667 bpi MFM serial cart. tape X3B5/86-199 (Read only) (CompacTape)
•= 16h - 10000 bpi MFM serial cart tape X3.193-1990 (Read only) (CompacTape
II)
•= 17h - 42500 bpi MFM serial cart tape X3B5/91-174 - 2.6 GB (CompacTape III)
•= 18h - (Same as 17h but with 56 track pairs vs. 24) - 6.0 GB (CompacTape III)
•= 19h - 62500 bpi, 64 track pairs, serial cart tape - 10 GB (CompacTape III)
•= 7Fh - No change from previous density (NOP)