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8.24.3 Parameter

HELP

Display the CCKD help information.

STATS

Display the current CCKD statistics.

OPTS

Display the current CCKD options.

option

Set a CCKD option. Multiple options may be specified, separated by commas with
no intervening blanks.

The CCKD options are:

COMP=n

Specifies the compression type to be used. This overrides the compression used
for all CCKD files. The default (-1) means don’t override the compression. Valid
compression types are:

-1 Default

0 None

1 Zlib

2 Bzip2

COMPPARM=n

Overrides the compression parameter. A higher value generally means more com-
pression at the expense of CPU and/or storage. The default (-1) means don’t over-
ride the compression parameter. The value of n can be from -1 and 9.

RA=n

Sets the Number of read ahead threads. When sequential track or block group
access is detected, some number (RAT=n) of tracks or block groups are queued
(RAQ=n) to be read by one of the read ahead threads. The default is 2, the value of
n can be a number from 1 to 9.

RAQ=n

Sets the size of the read ahead queue. When sequential track or block group
access is detected, some number (RAT=n) of tracks or block groups are queued in
the read ahead queue. The default is 4, the value of n can be a number from 0 to
16. A value of zero disables read ahead.

RAT=n

Sets the number of tracks or block groups to read ahead when sequential track or
block group access is detected. The default is 2, the value of ratn can be a number
from 0 to 16. A value of zero disables read ahead.

WR=n

Sets the number of writer threads. When the cache is flushed, updated cache en-
tries are marked write pending and a writer thread is signalled. The writer thread
compresses the track or block group and writes the compressed image to the emu-
lation file.

A writer thread is CPU-intensive while compressing the track or block group and
I/O-intensive while writing the compressed image. The writer thread runs one nicer
than the CPU thread(s). The default is 2, a value from 1 to 9 can be specified

GCINT=n

This is the number of seconds the garbage collector thread waits during an interval.
At the end of an interval the garbage collector performs space recovery, flushes the
cache and optionally ‘fsyncs’ the emulation file.

However, the file will not be ‘fsynced’ unless at least 5 seconds have elapsed since
the last synchronization (FSYNC). The default is 10 seconds. You can specify a