Pre-allocation Size Adjusting Methods for Preventing File Fragmentation

he 25th IEEE Symposium on Massive Storage Systems and Technologies (MSST2008) was held in Baltimore Maryland United States of America from Sep. 22nd to 25th, 2008. This conference covers discussions about massive storage and is long-established. The conference in this year, co-located five workshops: computing with massive and persistent data, digital archive preservation and sustainability, storage network architecture and parallel I/Os, key management, and security. The number of participants is beyond 200 people. So it was very attractive.

Systems Development Laboratory, Hitachi, Ltd. presented a paper titled "Pre-allocation size adjusting methods depending on growing fie size" at the 5th IEEE international workshop on storage network architecture and parallel I/Os (SNAPI2008) which is one of five workshops.

In general, contents like office documents, mails, and images are stored as files on the storage. Usually, each file is stored on continuous space on the storage. However, under the condition of high load, each file is sometimes stored on discontinuous space on the storage. This is called "file fragmentation". Once file fragmentation happens, the performance of storage access and the stability of storage system operation may decrease.

We presented the technologies for preventing the file fragmentation in the workshop. We focused on the size of file and proposed pre-allocation size adjusting methods. The proposed methods allocate spaces at small size when file size is small and allocate spaces at large size when file size is large. We showed the proposed methods considerably improve the level of file fragmentation in comparison with "fixed size pre-allocation methods" which is one of conventional method. We also showed the result that the proposed methods improve the performance of storage access. These results support the effectiveness of proposed methods for preventing file fragmentation.

(By Takaki Nakamura, Systems Development Laboratory)