Technical data

System Management Features
4.12 New System Parameters
In this case, the OpenVMS system allocates a total of approximately 6,291,456
bytes of nonpaged pool. Of this amount, the system divides 2,097,152 bytes
among the RADs that are not the base RAD. The system then assigns the
remaining 4,194,304 bytes to the base RAD.
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4.12.8 RAD_SUPPORT (Alpha)
RAD_SUPPORT enables RAD-aware code to be executed on systems that support
Resource Affinity Domains (RADs); for example, AlphaServer GS160 systems.
A RAD is a set of hardware components (CPUs, memory, and I/O) with common
access characteristics. For more information about using OpenVMS RAD
features, refer to the OpenVMS Alpha Partitioning and Galaxy Guide.
4.12.9 SHADOW_MAX_UNIT
SHADOW_MAX_UNIT specifies the maximum number of shadow sets that can
exist on a node. The setting must be equal to or greater than the number
of shadow sets you plan to have on a system. Dismounted shadow sets, unused
shadow sets, and shadow sets with no write bitmaps allocated to them are
included in the total.
This system parameter is not dynamic; that is, a reboot is required when you
change the setting.
The default setting on OpenVMS Alpha systems is 500; on OpenVMS VAX
systems, the default is 100. The minimum value is 10, and the maximum value
is 10,000.
Note that this parameter does not affect the naming of shadow sets. For example,
with the default value of 100, a device name such as DSA999 is still valid.
4.12.10 VCC_MAX_IO_SIZE (Alpha)
The dynamic system parameter VCC_MAX_IO_SIZE controls the maximum size
of I/O that can be cached by the Extended File Cache. It specifies the size in
blocks. By default, the size is 127 blocks.
Changing the value of VCC_MAX_IO_SIZE affects reads and writes to volumes
currently mounted on the local node, as well as reads and writes to volumes
mounted in the future.
If VCC_MAX_IO_SIZE is 0, the Extended File Cache on the local node cannot
cache any reads or writes. However, the system is not prevented from reserving
memory for the Extended File Cache during startup if a VCC$MIN_CACHE_SIZE
entry is in the reserved memory registry.
VCC_MAX_IO_SIZE is a DYNAMIC parameter.
4.12.11 VCC_READAHEAD (Alpha)
The dynamic system parameter VCC_READAHEAD controls whether the
Extended File Cache can use read-ahead caching. Read-ahead caching is
a technique that improves the performance of applications that read data
sequentially.
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The system actually rounds up to an even number of pages on each RAD. In addition, the
base RAD is never assigned a value less than the smaller of the value of NPAGEDYN
and 4 megabytes.
System Management Features 4–17