Quantum 10K II - Manual (Page 218)

SCSI Description
Quantum Atlas 10K II Ultra160/m SCSI Hard Disk Drives 5–151
5.26 READ LONG Command (3Eh)
The READ LONG command is used in conjunction with the WRITE LONG
command to allow the initiator to issue raw reads and writes of physical data blocks,
but address them as logical blocks with an assumed sector length of 512 bytes.
These two commands are used to verify the correction capability of the drive’s ECC
and to create a known kind and location to verify the drive’s recovery and bad sector
handling policies.
Bit
Byte
7 6 5 4 3 2 1 0
0 Operation Code (3Eh)
1 Reserved Correct RelAdr
2 - 5 Logical Block Address
6 Reserved
7 - 8 Byte Transfer Length (562)
9 Control
Figure 5–69 READ LONG Command Descriptor Block — Data Format
Table 5–71 READ LONG Command Descriptor Block — Field Descriptions
Field Description
Correct When the value in this field is 1, the drive corrects the data by the ECC
before transferring it to the initiator. When the value is 0, the drive does
not perform ECC correction on the data.
NOTE: This bit, not the DCR bit of the Read Recovery page, governs the
effect of error correction for the READ LONG command.
RelAdr Relative addressing is not supported by the drive. This value must be 0.
Logical Block Address Specifies the logical sector to read.
Byte Transfer Length Must be 562. This value reflects the number of bytes spanned by the
ECC, including the ECC itself, rounded up to the next word
(this is easiest understood in bits: 4096 data bits + 1 force error bit +
15 Logical Block Address bits + 16 cross check bits + 2 pad bits + 360
ECC bits + 6 pad bits that are not written to media but are only needed
for transfer = 4496 bits or 562 bytes). Any other value in this field results
in a CHECK CONDITION status and the appropriate sense data.