Some OSs offer a choice of file system block sizes. For file systems supporting Oracle datafiles, the block size should be 8KB when compression is used. When compression is not required, a block size of either 8KB or 4KB can be used.

If a datafile is placed on a file system with a 512-byte block, misaligned files are possible. The LUN and the file system might be properly aligned based on NetApp recommendations, but the file I/O would be misaligned. Such a misalignment would cause severe performance problems.

File systems supporting redo logs must use a block size that is a multiple of the redo block size. This generally requires that both the redo log file system and the redo log itself use a block size of 512 bytes.

At very high redo rates, it is possible that 4KB block sizes would perform better because high redo rates allow I/O to be performed in fewer and more efficient operations. If redo rates are greater than 50MBps, consider testing a 4KB block size.

A few customer problems have been identified with databases using redo logs with a 512-byte block size on a file system with a 4KB block size and many very small transactions. The overhead involved in applying multiple 512-byte changes to a single 4KB file system block led to performance problems that were resolved by changing the file system to use a block size of 512 bytes.