LDKBMWND parameter

# of pages in DKBM-BTB anticipatory write window

Summary

Default value

(version 7.4 and earlier) NSERVS plus 1.

(version 7.5 and later) A minimum of ( 0.5 * NUMBUF ).

MINBUF, MAXBUF, and/or NUMBUF will first be adjusted according to this formula:
NLRUQ * ((NSERVS + NSUBTKS) * MAXOBUF + 15)

Following that, if a value for LDKBMWND is specified in CCAIN and that value 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

An anticipatory write window that starts writes for any modified 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).

Refer to Disk buffer monitor statistics and parameters and Disk buffers and Model 204 storage for more information about disk buffers.