Solaris™ Internals: Core Kernel Components

15.1. Introduction to File Caching

Traditional Unix implements file system caching in the I/O subsystem by keeping copies of recently read or written blocks in a block cache. This block cache sits just above the disks, and it caches data corresponding to physical disk sectors.

Figure 15.1 shows an example in which a process reads a piece of a file. The process reads a segment of a file by issuing a read system call into the operating system. The file system must then look up the corresponding disk block for the file by looking up the block number in the direct/indirect blocks for that file, after which the files system requests that block from the I/O system. The I/O system retrieves the block from disk the first time; then, the file systems ...