cached I/O vs direct I/O

cached I/O

direct I/O

1. Application issues a read request
2. Kernel looks for requested data in file buffer cache
3. Requested data not present in file buffer cache
4. Kernel reads data from disk
5. Read data is cached in file buffer cache
6. Read data is copied from file buffer cache to applicatio buffer

1. Application issues a read request
2. Kernel initiates a disk request
3. Requested data transfered from disk to application buffer