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Startup Command and Parameter Reference
Startup Parameter Descriptions : Direct I/O (-directio)

Direct I/O (-directio)

Use Direct I/O (-directio) to open all files in unbuffered mode, which enables OpenEdge to use an I/O technique that bypasses the operating system buffer pool and transfers data directly from a buffer to disk.
Operating system and syntax
UNIX / Windows
Use with
Maximum value
Minimum value
Single-user default
Multi-user default
Client Connection, Database Server
Not enabled
Not enabled
This technique has several advantages over buffered reads and writes, such as avoiding the overhead of maintaining the operating system buffer pool and eliminating competition for operating system buffers between OpenEdge programs and other programs. The operating system buffer-pool algorithms are designed for efficient sequential file access; the OpenEdge buffer-pool algorithms are more efficient for access to an OpenEdge database.
You might improve OpenEdge performance by using the direct I/O feature. To use direct I/O, use Blocks in Database Buffers (-B) to increase the size of the OpenEdge buffer pool, since OpenEdge I/O does not pass through the operating system buffer pool. Also, decrease the size of the operating system buffer pool to compensate for the additional memory allocated to OpenEdge.
Note: Use asynchronous page writers (APWs). They improve database performance by performing overhead operations in the background.