Notes:

raq should be at least as large as ra. Read ahead threads are scheduled from entries in the read
ahead queue. Likewise rat should not exceed raq because only raq tracks or block groups can be
queued at any time.
The number of writer threads wr should usually be 1 more than the number of host processors.
This is because one writer thread could be CPU-bound (compressing a track or block-group
image) and the other could be i/o-bound (writing the compressed image).
The garbage collection interval governs the maximum time in seconds an updated track or block
group image will reside in storage before being written to the emulation file. A large value may
mean more data loss if a catastrophic error occurs. A small value may mean that more CPU time
is spent compressing images.

For example, suppose that a particular image is updated several times each second. If the inter-
val is changed from the default 5 seconds to 1 second, then that image will be compressed and
written 5 times more frequently. A large value may cause more cache flushes within a garbage
collection interval. These kinds of flushes mean that a read will wait because there are no avail-
able cache entries, slowing the emulated operating system. A large value will also cause more
pending free space to build up (since free space is flushed each interval). This may mean that the
garbage collector space recovery routine will perform more work and the resulting emulation file
may be larger.
Specify fsync=1 and gcint=5 if you are seriously concerned about your data being lost due to a
failure. fsync will ensure your data on disk is coherent. However, fsync may cause a noticeable
performance degradation. Note that an fsync will not be performed more often than every 5
seconds.

5.10.4 Examples

Example 1:

Set the CCKD options to use bzip2 as compression method and using maximum compression.

CCKD COMP=2,COMPPARM=9

Example 2:

Set the CCKD options to use the default compression method, as well as default compression. Disable
stressed writes and set the number of trace entries to 100000.

CCKD COMP=-1,COMPPARM=-1,NOSTRESS=1,TRACE=100000

5.11 CMDLEVEL (Set current command group)

5.11.1 Function

The CMDLEVEL system parameter sets the current command group(s). A plus sign preceding the com-
mand group activates the console commands of this group, whereas a preceding minus sign deactivates
the commands.

A table showing the affiliation of each console command to the various command groups can be found in

Appendix D. Hercules Command Groups .

Some console commands are always active to keep Hercules operable, independent of the current active
command group. These commands are listed under command group 'NONE' in the above mentioned
table. Command group ‘NONE’ is the result of a ‘CMDLVL –ALL’ command.

The default command level is set to operator, maintenance, programmer and configuration (which corres-
ponds to the command "CMDLEVEL -ALL +OPER +MAINT +PROG +CONFIG"). Some of the arguments
can be abbreviated as shown in the syntax section below.

5.11.2 Syntax

Descriptive

- rammer


oper

Diagram




~¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬¬®

+ ¬¬¬¬¬¬¬¬¬ÊÍ




-
¬¬¬ ¬¬¬¬«






¬¬¬¬¬¬¬¬¬¬¬«






¬¬¬¬¬«






¬¬¬«






¬¬¬¬¬¬¬«






¬¬¬¬¬¬¬¬¬

5.11.3 Parameter

+

The plus sign activates the commands of the following command group.

-

The minus sign deactivates the commands of the following command group.

ALL

Command group ‘ALL’ contains all Hercules console commands. Specifying com-
mand group ‘+ALL’ enables all console commands whereas command group ‘-ALL’
equals to NONE. This disables all console commands with the exception of com-
mands necessary to keep Hercules operable.

Previous Page Next Page