It is known that ZFS dRAID [2] provides random data blocks permutation and reconstruction speed up is getting its boost with this initial condition. The question we tried to answer is if there some special permutation that would optimize reconstruction speed at theoretical maximum. We introduce our solution with the usage of cyclic matrices of data layout as currently the best found way to get maximum benefit out from initial declustered RAID configuration.

This paper presents on-line algorithm that determines further datapath for incoming requests - should they temporarily stay in RAM buffers for future merge operation or should they be written to disks immediately. With workload analysis in real time, the delay time spent in RAM buffer is a self-tuned parameter. This approach increases sequential write requests latency but sufficiently raises the overall performance of sequential write workloads without the use of expensive non-volatile cache.

HPC runs in a distributed structure with a single shared pool of data. In our case, the distributed structure is Lustre file system [4], and the single shared pool of data is our declustered HDD RAID (denoted as DCR). To increase performance, it is suggested to use Open CAS technology [3] as a cache on RAM/NVDIMM with special parameters, optimized for heavy data-intensive sequential HPC workload and an online-algorithm which reduces the number of RMW operations, by merging sequential requests into one full-stripe one.