Enabling asynchronous disk I/O

Sybase recommends that you do not use block devices on UNIX and Linux systems. A system crash may lead to loss of data integrity if you use block devices as database devices.

To verify that the async I/O is active on the Itanium machine:

1. Log in as root.

2. Issue the command:

   # kcmodule -a | grep aync
   

   Result: asyncdsk static required

   or you can also use the following:

   # ls /dev/asyn*
   idev/async /dev/asyncdsk
   

It is mandatory for HP-UX users to enable asynchronous I/O.

To improve I/O performance on character or raw block devices, enable asynchronous I/O by installing the HP asynchronous I/O driver from SAM. For help with installing this driver, contact your operating system administrator or HP technical support.

1. To launch the Kernel Configuration use kcweb -F.

2. Select Modules.

3. Select asyncdsk and change the next boot to static.

4. Rebuild the kernel, and reboot the system.

5. Execute the following commands using the userid root:

   #/etc/mknod/dev/async c 101 4
   #chmod 0660/dev/async
   #chown <uid> /dev/async
   #/etc/setprivgrp <ugrp> MLOCK
   

   Where:

   <uid> is the identification (user ID) used by the user that is booting Adaptive Server.

   <ugrp> is the user group for the sybase userid.

6. At the UNIX prompt, execute the following statements as “root”. The user ID of the user who is starting Adaptive Server and Backup Server must be the owner of the /dev/async directory.

It is mandatory for HP-UX users to enable asynchronous I/O.

To improve I/O performance on character or raw and block devices, enable asynchronous I/O by installing the HP asynchronous I/O driver from SAM. For help with installing this driver, contact your operating system administrator or HP technical support.

To enable asynchronous I/O:

1. From the SAM Kernel Configuration menu, choose Drivers and set the Pending State for asyncdisk to In by adding the driver.

   An alternate step could be done by adding the asyncdsk subsystem keyword to /stand/system.

2. Rebuild the kernel, and reboot the system.

3. Execute the following commands using the userid root:

   #/etc/mknod/dev/async c 101 4
   #chmod 0660/dev/async
   #chown <uid> /dev/async
   #/etc/setprivgrp <ugrp> MLOCK
   

   Where:

   <uid> is the identification (user ID)used by the user that is booting Adaptive Server.

   <ugrp> is the user group for the <uid> user ID.

4. At the UNIX prompt, execute the following statements as “root”. The user ID of the user who is starting Adaptive Server and Backup Server must be the owner of the /dev/async directory.

Enable asynchronous disk I/O.

This step is mandatory for IBM users.

Enable asynchronous I/O by adjusting the kernel parameters, using the System Management Interface Tool (SMIT):

If your system uses more than seven disks at the same time for Asynchronous I/O, increase the MAXIMUM number of servers value by 1 for every active device.