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ST43401N/ND and ST43402ND Reference Manual, Rev. C
Using the sweep cycle function
The sweep cycle is a feature that periodically moves the heads to different
locations on the discs during intervals when the drive is idle. The following are
highlights of the sweep cycle function:
• Using the sweep cycle enhances drive reliability. We encourage you either
to enable the drive sweep cycle or to use a sweep cycle controlled by the
host (initiator). Consult with an analyst in making this choice.
• The sweep routine consumes approximately 11 seconds of a 13-hour
period. The drive is available to the system more than 99.98 percent of the
time.
• You may disable the sweep cycle (described below) without affecting the
specified mean time between failures (MTBF) or warranty agreements.
The drive is preset during manufacturing with the sweep cycle option selected.
A jumper on the control board makes the selection, as shown in Figure 10. The
other jumpers on the control board are discussed in the user's manual.
The jumper is identified as Sweep Cycle Option, which either enables or
disables the sweep cycle function. The jumper can be positioned as follows:
• Jumper disconnected—disables the sweep cycle function
• Jumper connected—enables the sweep cycle function
Sweep movements, if enabled, can occur only in conjunction with seeks
required by the controller or with any SCSI read or write operation having an
implied seek. Each time the drive performs a sweep cycle, it starts a 12-minute
timeout. When the timeout has elapsed, the drive performs another sweep
cycle only when it receives the Seek command. When combining a sweep
cycle with a seek, the drive performs the sweep cycle first and then executes
the Seek command.
If a sweep segment was initiated by the Seek command, the drive performs
the sweep function and then moves the heads to the cylinder requested by the
controller. If about 15 minutes elapse with no disc access commands received
from the SCSI bus, the SCSI I/O logic sends a one-track seek command to the
drive logic. This command causes the drive to perform its sweep cycle.
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