SALIUS - serviço de armazenamento estável com recuperação para frente baseado na replicação remota de buffers.

Abstract

Stable storage of data is an important requirement for many applications. Traditional file systems use synchronous writing to disk as a way of guaranteeing the stability of stored data. However, synchronous writing impairs application performance because of the slow speed of disk access. As hardware technology advances, impairment to performance caused by the use of synchronous writing increases. The hardware component technologies develop at varying rates. The speed of processors is increasing at a greater rate than the speed of disk access. Thus disk access time is limiting the performance of applications which perform many disk access operations, especially in the case of synchronous writing. This dissertation presents the specification of a new stable storage technique, called SALIUS — STABLE STORAGE SERVICE WITH FORWARD RECOVERY BASED ON REMOTE REPLICATION OF BUFFERS. The proposed service substitutes synchronous writing with remote replication of buffers that are modified in the cache. In this way the application does not wait for output to disk but instead waits for the sending of modified data through a network and the storage of this data in the main memory of a remote machine. The main advantage of the proposed service is the guarantee of stability, with a potentially better performance than the solutions based on synchronous writing, due to the fact that the speed of memory access is progressively greater than that of disk access, and the transfer of data through a high speed network is considerably faster than writing the same quantity of data to disk. Since memory and network technologies are developing at a considerably greater speed than that of disk technology, this approach could be even more advantageous. To assure the stability of the information, the technique includes a forward recovery mechanism which allows it to collect enough remote information to restore the file system to a consistent state after a crash.