Product manual

67
Web-based Management
aDvanCED ConFiguration oPtions For thE FiLE systEM
In order to better understand how changing the Block Size, Journal Size and Inode Ratio can change the
performance of the File System, please read the description of these settings below.
Block Size: This is the smallest amount of disk space that can be allocated by the le system. It cannot be
changed once the le system has been created. Changing the Block Size value (also known as Block Allocation
Size ) can degrade or improve performance depending on what critical applications are likely to use the le
system. In general, applications that typically use large sized les, will work better if the le system allocates
larger sized blocks, and applications that use small sized les are better off using smaller block sizes.
As an example, 256 blocks are needed in order to store a 1MB sized le on a le system with a block size of
4KB. Since there are many blocks used, it is more likely that the blocks will be located in non-contiguous blocks,
the le will be fragmented. When many les are fragmented, this can degrade performance. So having a block
size that is smaller than most of the les on the le system can result in greater fragmentation and reduce I/O
throughput. Performance is also impacted because the le must be allocated across many blocks, an operation
that uses processing resources.
In another example, we can use values that are the reverse of the previous example with a 4KB le on a le
system with a 1MB block size. In this case, there is an inefciency of the disk space allocation since there is 1020K
of unused space on the block. So if most les are smaller than the block size, much of the disk space can be
wasted, but the le is not fragmented or allocated across many blocks, so performance is not affected.
The larger block size means there will be fewer allocations, using less le system overhead in the form of
metadata, and less fragmentation since the large les are more likely to be allocated on contiguous blocks. If
a small block size is used for large les, the large les will be allocated to many more blocks (requiring more
metadata entries) and will be more likely to be fragmented (not placed contiguously on the disk). However, using
a large block size for applications that generally use small sized les results in inefcient use of disk space.
Note
The default le system conguration settings for the Advanced le
system creation option, and the conguration settings used for the
Automatic option are best suited for audio and video applications.