File system attributes that affect performance
The longer a file system is used, the more fragmented it becomes. With the dynamic allocation of resources, file blocks become more and more scattered, logically contiguous files become fragmented, and logically contiguous logical volumes (LV) become fragmented.
The following list of things occur when files are accessed from a logical volume that is fragmented:
- Sequential access is no longer sequential
- Random access is slower
- Access time is dominated by longer seek time
However, once the file is in memory, these effects diminish. File system performance is also affected by physical considerations, such as:
- Types of disks and number of adapters
- Amount of memory for file buffering
- Amount of local versus remote file access
- Pattern and amount of file access by application
JFS allows you to change the file system fragment size for better space utilization by subdividing 4 KB blocks. The number of bytes per i-node, or NBPI, is used to control how many i-nodes are created for a file system. Compression can be used for file systems with a fragment size less than 4 KB. Fragment size and compression affect performance and are discussed in the following sections: