Sun Java System Application Server Enterprise Edition 8.1 2005Q2 Performance Tuning Guide

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### Placing HADB files on Physical Disks

For best performance, data devices should be allocated on separate physical disks. This applies if there are nodes with more than one data device, or if there are multiple nodes on the same host.

Place devices belonging to different nodes on different devices. Doing this is especially important for Red Hat AS 2.1, because HADB nodes have been observed to wait for asynchronous I/O when the same disk is used for devices belonging to more than one node.

An HADB node writes information, warnings, and errors to the history file synchronously, rather than asynchronously, as output devices normally do. Therefore, HADB behavior and performance can be affected any time the disk waits when writing to the history file. This situation is indicated by the following message in the history file:

    BEWARE - last flush/fputs took too long

To avoid this problem, keep the HADB executable files and the history files on physical disks different from those of the data devices.

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