USER RESPONSIBLE F O R V E R I F Y I N G VERSION A N D COMPLETENESS
O E M F U N C T I O N A L SPECIFICATION ULTRASTAR X P (DFHC) SSA M O D E L S 1.12/2.25 GB - 1.0" H I G H
Table 9. Track (or Head) Skew for several block lengths
3.6 Idle Time Functions
The execution of various functions by the drive during idle times may result in delays of commands
requested by initiators. ‘Idle time’ is defined as time spent by the drive not executing a command requested
by a initiator. The functions performed during idle time are:
1. Servo R u n Out Measurements
2. Servo Bias Measurements
3. Predictive Failure Analysis (PFA)
4. Channel Calibration
5. Save Logs and Pointers
6. Disk Sweep
The command execution time for commands received while performing idle time activities may be increased
by the amount of time it takes to complete the idle time activity. The messages and data exchanged across
the SSA link are not affected by idle time activities.
Note: Command Timeout Limits do not change due to idle time functions.
All Idle Time Functions have mechanisms to lessen performance impacts for critical response time periods of
operation. And in some cases virtually eliminate those impacts from an Initiator's point of view. All Idle
Time Functions will only be started if the drive has not received a SCSI command for at least 5 seconds (40
seconds for Sweep). This means that multiple SCSI commands are accepted and executed without delay if
the commands are received by the drive within 5 seconds after the completion of a previous SCSI command.
This mechanism has the benefit of not requiring special system software (such as issuing SCSI Rezero Unit
commands at known & fixed time intervals) in order to control if and when this function executes.
Note:
Applications which can only accommodate Idle Time Function delays at certain times, but can not
guarantee a 5 second re-instruction period, may consider synchronizing idle activities to the system needs
through use of the L I T F bit in Mode Select Page 0, and the Rezero Unit command. Refer to the Ultrastar
XP ( D F H C ) S S A Models Interface Specification for more details
Following are descriptions of the various types of idle functions, how often they execute and their duration.
Duration is defined to be the maximum amount of time the activity can add to a command when no errors
occur. N o more than one idle function will be interleaved with each command.
Following the descriptions is a summary of the possible impacts to performance.
Notch #
User bytes / logical
block
1
2
3
4
5
6
7
8
9
10
256
20
20
20
19
19
17
17
17
17
15
512
13
13
13
12
12
11
11
10
10
10
520
12
12
12
12
11
11
10
10
10
10
522
12
12
12
12
11
11
10
10
10
9
524
12
12
12
12
11
11
10
10
10
9
528
12
12
12
12
11
11
10
10
10
9
600
11
11
11
11
10
10
10
9
9
9
688
10
10
10
10
9
9
9
9
8
8
744
9
9
9
9
9
9
8
8
8
7
Note: Contact an IBM Customer Representative for values at other formatted block lengths.
Source filename=PERFORM
IBM Corporation
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