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General System Resource Management 119

To turn off access time updates, mount the file system with the noatime option. To

do so, either edit /etc/fstab directly, or use the Fstab Options dialog when editing

or adding a partition with the YaST Partitioner.

9.3.3 Prioritizing Disk Access with ionice

The ionice command lets you prioritize disk access for single processes. This en-

ables you to give less I/O priority to non time-critical background processes with

heavy disk access, such as backup jobs. On the other hand ionice lets you raise I/O

priority for a specific process to make sure this process has always immediate access

to the disk. You may set the following three scheduling classes:

Idle

A process from the idle scheduling class is only granted disk access when no oth-

er process has asked for disk I/O.

Best effort

The default scheduling class used for any process that has not asked for a specific

I/O priority. Priority within this class can be adjusted to a level from 0 to 7 (with

0 being the highest priority). Programs running at the same best-effort priority

are served in a round-robin fashion. Some kernel versions treat priority within the

best-effort class differently—for details, refer to the ionice(1) man page.

Real-time

Processes in this class are always granted disk access first. Fine-tune the priority

level from 0 to 7 (with 0 being the highest priority). Use with care, since it can

starve other processes.

For more details and the exact command syntax refer to the ionice(1) man page.

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Red Hat ENTERPRISE LINUX 5.4 - SYSTEMTAP BEGINNERS GUIDE Informazioni Techniche Pagina 133