User Manual

SCSI Commands Reference Manual, Rev. J 464
www.seagate.com Parameters for direct access devices
SCSI-2 bit
1 When set to one, the SCSI-2 bit changes the following SCSI-3 features from their SCSI-3 definition to the SCSI-2 definition:
a) Control Mode Page (0Ah) Length from 0Ah to 06h; and
b) Caching Page (08h) Length from 12h to 0Ah.
0 When S2 is set to zero, all features remain as specified in other portions of this specification.
DAR (Deferred Auto Reallocation) bit
1 Deferred reallocation is enabled. When an unrecoverable read error occurs, the drive remembers the LBA of the error; when a subse-
quent write command occurs for that LBA and the AWRE bit in mode page 1 is enabled, then the LBA is reallocated before the write
command is completed.
0 Deferred reallocation is disabled.
Self Seek bit
1 If the Self Seek bit is set to one, the drive will enter self seek mode for testing purposes. Such testing could include, but is not limited to,
power dissipation and acoustics. While in this mode, the drive will accept SCSI commands and will process them in between the self
seek operations, including a MODE SELECT to turn this bit back off. As such, this bit should be off for normal drive operations.
0 If this bit is set to zero, the drive will not self seek; normal operating mode.
VJIT Disabled bit
1 When this bit is set to 1, the drive will always use the fastest seek type (i.e., JIT 0). JIT bits 0:3 of byte 4 are ignored.
0 When this bit is set to 0, the drive will operate according to the settings of JIT bits 0:3.
JIT (Just in Time) bits
The four JIT (Just In Time) bits allow you to enable and disable certain seek speeds. JIT0 represents the fastest seek type used by the drive, JIT1
represents the second fastest, JIT2 represents the third fastest, and JIT3 represents the slowest seek type. You can use these bits to reduce
acoustics by disabling the fastest seeks. This can also reduce power consumption (from seek activity). These JIT settings only affect user read
and write operations. Background drive operations and user seek commands will always use the fastest seek type. When the bit is set to 1, the
drive is allowed to use this seek type and any slower seek types in its seek speed algorithm. When the bit is set to 0, the drive is not allowed to
use this seek type in its seek speed algorithm unless a faster seek type is selected. If all JIT bits are set to zero or if all bits are set to one, the drive
can use any of the seek speeds.
COMMAND AGING LIMIT field
The COMMAND AGING LIMIT field specifies the maximum time, in milliseconds, that a command is allowed to languish in the command queue
before it is marked as the next command to be processed.