Direct I/O is a method
for processing input and output files and is used in file handling.
Direct
I/O enables SAS to
read files from and write files directly to storage devices without
first going through the UNIX operating environment's read and write
caches. You can use direct
I/O for SAS files. Using direct
I/O might improve system performance, depending on the number and types
of jobs that you are running.
SAS uses three related
options that affect direct
I/O:
-
ENABLEDIRECTIO statement option
-
USEDIRECTIO= statement option
-
USEDIRECTIO= data set option
The ENABLEDIRECTIO option
in the LIBNAME statement makes direct
I/O processing available for data sets that are listed
in the DATA statement. The libref that points to the data sets must
have been defined in a LIBNAME statement that uses the ENABLEDIRECTIO
option. Using ENABLEDIRECTIO itself does not turn on direct
I/O.
A libref that is assigned
to a directory with the ENABLEDIRECTIO option will not match another
libref that is assigned to the same directory without the ENABLEDIRECTIO
option. The two librefs will point to the same directory, but the
files that are opened using the libref with ENABLEDIRECTIO can be
read from and written to using direct
I/O. Files that are opened using the other libref will
be read from and written to using the regular disk
I/O calls.
The USEDIRECTIO= data
set option in the DATA statement or the USEDIRECTIO= statement option
in the LIBNAME statement turns on direct
I/O for data sets in which the ENABLEDIRECTIO statement
option has been applied. Using USEDIRECTIO= without first applying
the ENABLEDIRECTIO option has no effect on direct
I/O in a data set.