Enabling Asynchronous Disk I/O on Linux

Enable asynchronous I/O on Linux.

Prerequisites

Before starting SAP ASE, verify there are sufficient system resources for kernel asynchronous I/O.

The total number of system-wide reservable I/O descriptors (aio-max-nr) minus the current number of descriptors reserved by all processes (aio-nr) must be sufficient to accommodate the value for max async i/os per engine.

Task

To determine the values for aio-max-nr and aio-nr, use:
```
cat /proc/sys/fs/aio-max-nr
cat /proc/sys/fs/aio-nr
```
Modify the number of reservable descriptors by setting fs.aio-max-nr with the sysctl operating system command. See your operating system documentation for information.
SAP ASE may issue messages similar to these in the error log if there are insufficient number of I/O descriptors during start-up, or when an engine is brought online:
```
kernel KAIO not initialized because the requested number of async I/Os(%d) will exceed the resources available on the operating system.

kernel Kernel asynchronous I/O not initialized. The io_setup() system call returned %d.
```
See max async i/os per engine in Setting Configuration Parameters in the System Administration Guide, Volume 1.