File System, Logical Volume, and Disk I/O Performance

This chapter focuses on file system tuning and the performance of locally attached disk drives.

If you are not familiar with the operating system concepts of volume groups, logical and physical volumes, and logical and physical partitions, read Performance Overview of Fixed-Disk Storage Management.

File-system configuration has a large effect on overall system performance and is time-consuming to change after installation. Deciding on the number and types of hard disks, and the sizes and placements of paging spaces and logical volumes on those hard disks, is therefore a critical preinstallation process. For an extensive discussion of the considerations for preinstallation disk configuration planning, see Disk Preinstallation Guidelines.

The following sections are presented in this chapter:

• Monitoring Disk I/O
• Monitoring and Tuning File Systems
• File System Types
• Differences Between JFS and Enhanced JFS
• Potential Performance Inhibitors for JFS and Enhanced JFS
• Performance Enhancements
• Summary of Tunable Parameters
• Changing File System Attributes that Affect Performance
• Changing Logical Volume Attributes That Affect Performance
• Physical Volume Considerations
• Volume Group Recommendations
• Reorganizing Logical Volumes
• Reorganizing File Systems
• Reorganizing JFS Log and Log Logical Volumes
• Tuning with vmtune
• Using Disk-I/O Pacing
• Tuning Logical Volume Striping
• Tuning Asynchronous Disk I/O
• Tuning Direct I/O
• Using Raw Disk I/O
• Using sync/fsync Calls
• Setting SCSI-Adapter and Disk-Device Queue Limits
• Expanding the Configuration
• Using RAID
• Using SSA
• Using Fast Write Cache