Performance Impacts with Reliable Parallel File Systems at Exascale Level

The introduction of Exascale storage into production systems will lead to an increase on the number of storage servers needed by parallel file systems. In this scenario, parallel file system designers should move from the current replication configurations to the more space and energy efficient erasure-coded configurations between storage servers. Unfortunately, the current trends on energy efficiency are directed to creating less powerful clients, but a larger number of them (light-weight Exascale nodes), increasing the frequency of write requests and therefore creating more parity update requests. In this paper, we investigate RAID-5 and RAID-6 parity-based reliability organizations in Exascale storage systems. We propose two software mechanisms to improve the performance of write requests. The first mechanism reduces the number of operations to update a parity block, improving the performance of writes up to 200%. The second mechanism allows applications to notify when reliability is needed by the data, delaying the parity calculation and improving the performance up to a 300%. Using our proposals, traditional replication schemes can be replaced by reliability models like RAID-5 or RAID-6 without the expected performance loss.