The Question is:
I would like to raise the VMS Virtual I/O cache from the default 3200 kbyte.
Which sysgen parameter controls this?
Will the usual modparams.dat/autogen do the trick.
The Answer is :
On OpenVMS Alpha V6.1 and above, the Virtual I/O Cache size is controlled
by the SYSGEN parameter VCC_MAXSIZE. Although there are other VCC parameters,
all except VCC_MAXSIZE are reserved to Compaq and should not be changed.
Set a value for VCC_MAXSIZE in MODPARAMS.DAT, as for any SYSGEN parameter,
and execute AUTOGEN. The new cache size will be realised on the next reboot.
Also note that the unit for VCC_MAXSIZE is in BLOCKS, while the SHOW MEM
display shows units of kilobytes. Thus, the default value for VCC_MAXSIZE
is 6400 yields a cache size of 3200 kilobytes. Be careful in choosing
values to make sure you select the right units -- the different units have
been known to cause confusion.
The maximum VIOC cache size is also limited by the available space in S0
and S1 system space (traditional thirty-two bit system space).
The SDA command CLUE MEMORY/LAYOUT can be of interest here.