ZioLib: A parallel I/O library

Yang, Woo-Sun ; Ding, Chris

Lawrence Berkeley National Laboratory

关键词: Efficiency;    Implementation;    Dimensions;    Performance;    99 General And Miscellaneous//Mathematics, Computing, And Information Science;   

DOI  :  10.2172/819966
RP-ID  :  LBNL--53521
RP-ID  :  AC03-76SF00098
RP-ID  :  819966

美国|英语

来源: UNT Digital Library

【 摘 要 】

In a distributed memory parallel environment, many applications rely on a serial I/O strategy, where the global array is gathered on a single MPI process and then written out to a file. I/O performance with this approach is largely limited by single process I/O bandwidth. Even when parallel I/O is used, satisfactory parallel scaling is not always observed. It is because in many applications fields are not necessarily in a most favorable parallel decomposition for I/O. The best I/O rates are obtained when a field is decomposed with respect to the array's last dimension (referred to here as Z). Another situation often encountered in many applications is that a field in CPU resident memory is in one index order but must be stored in a disk file in another order. Changing index orders can complicate a parallel I/O implementation and slow down I/O. ZioLib facilitates an efficient parallel I/O for arrays in such situations. In case of a write, ZioLib remaps a distributed field into a Z-decomposition on a subset of processes (which will be called the I/O staging processes) and from there writes to a disk file in parallel. In this Z-decomposition, the data layout of the remapped array on the staging processes memory is the same as on disk, thus only block data transfer occurs during parallel I/O, achieving maximum efficiency. In case of a read the steps are reversed to build the required distributed arrays on the computational processes.