LDKBMWND parameter

# of pages in DKBM-BTB anticipatory write window

Summary

Default value

V7.4 and earlier: NSERVS plus 1

V7.5 and later: A minimum of ( 0.5 * NUMBUF )

V7.7 and later: If NUMBUFG is greater than 0, LDKBMWND is ignored

Before the value of LDKBMWND is adjusted or recalculated, the minimum size of NUMBUF must first be determined by this formula:

NLRUQ * ((NSERVS + NSUBTKS) * MAXOBUF + 15)

If the current value of NUMBUF exceeds this value and is a multiple of NLRUQ, no further adjustments to NUMBUF are made.

Following that, if a value for LDKBMWND is specified in CCAIN and is greater than 0.5*NUMBUF, the value can still be adjusted:

• The final value must be an even multiple of NLRUQ
• The final value must not be greater than NUMBUF minus the total number of buffers that might possibly be open at any one time:

  NUMBUF - (((NSERVS+NSUBTKS)*MAXOBUF)+14)*NLRUQ

Parameter type

System

Where set

On User 0's parameter line by system manager

Related products

All

Introduced

Model 204 V6.1 or earlier

Description

LDKBMWND specifies an anticipatory write window that starts writes for any modified below-the-bar buffers that enter the window.

When an anticipatory write for a modified buffer completes, the buffer is immediately reusable.

High values of LDKBMWND might unnecessarily increase the number of writes done (measured by the DKWR statistic). Low values might cause excessive waiting for buffers (measured by the DKSWAIT statistic).

See also

• Disk buffer monitor statistics and parameters and Disk buffers and Model 204 storage, for more information about anticipatory write windows and disk buffers
• LDKBMWNG