Improved data layouts for fault tolerant multimedia systems

Multimedia servers typically rely on multiple disks for the storage of multimedia data, so they are more vulnerable to disk failures. To guarantee continuous service during disk failure, parity data is stored on-disk and then used to reconstruct missing data. Data pages are clustered into groups and for each group a parity page is computed by applying bitwise exclusive-or over the data pages in the group. The data and parity pages in a group are stored on different disks. If a disk fails then the system can reconstruct a page on the faulty disk by applying bitwise exclusive-or to the other data pages in the group and the parity page. However, retrieving the parity and data pages imposes additional demands on the operational disks. We propose two grouping techniques that aim to minimize the overhead of retrieving the other pages in the parity group. These techniques cluster pages that are likely to be retrieved simultaneously into one parity group. By integrating our grouping techniques with BIBD-based data placement, we produce fault-tolerant layouts for multimedia data. These layouts were evaluated and compared with the declustered parity scheme using a simulation study. Our results show that one of our techniques reduces the average retrieval overhead by a factor of 1.3 to 15