PRIMECLUSTER Global File Services Configuration and Administration Guide 4.1 (Linux)

1.4.2 Contiguous block assignment

The GFS Shared File System assigns contiguous blocks to file data to take better advantage of batch I/O processing to improve the file system performance. The GFS Shared File System manages area on the extent-base for assigning contiguous blocks. For the range of blocks that can be acquired contiguously, the file system manages area assignment using a file offset, a start block number, and the number of blocks used.

The file system also takes into consideration the possibility of contiguous block assignment when extending the file.

Following picture shows a block assignment example that a file has three extents which locate 0, 64MB, 96MB file offset and 64MB, 32MB, 4MB extent length respectively.

[Figure Contiguous block assignment]

Empty file data areas are also managed in the extent base to implement high-speed assignment of optimum empty areas.