Administrator Guide

Performance characterization
21 Dell EMC Ready Solution for HPC PixStor Storage | Document ID
Figure 9 N to N Sequential Performance
From the results we can observe that performance rises very fast with the number of clients used and then
reaches a plateau that is stable until the maximum number of threads that IOzone allow is reached, and
therefore large file sequential performance is stable even for 1024 concurrent clients. Notice that the
maximum read performance was 23 GB/s at 32 threads and very likely the bottleneck was the InfiniBand EDR
interface, with ME4 arrays still had some extra performance available. Similarly notice that the maximum write
performance of 16.7 was reached a bit early at 16 threads and it is apparently low compared to the ME4
arrays specs.
Here it is important to remember that GPFS preferred mode of operation is scattered, and the solution was
formatted to use it. In this mode, blocks are allocated from the very beginning in a pseudo-random fashion,
spreading data across the whole surface of each HDD. While the obvious disadvantage is a smaller initial
maximum performance, that performance is maintained fairly constant regardless of how much space is used
on the file system. That in contrast to other parallel file systems that initially use the outer tracks that can hold
more data (sectors) per disk revolution, and therefore have the highest possible performance the HDDs can
provide, but as the system uses more space, inner tracks with less data per revolution are used, with the
consequent reduction of performance.
Sequential IOR Performance N clients to 1 file
Sequential N clients to a single shared file performance was measured with IOR version 3.3.0, assisted by
OpenMPI v4.0.1 to run the benchmark over the 16 compute nodes. Tests executed varied from single thread
up to 1024 threads.
Caching effects were minimized by setting the GPFS page pool tunable to 16GiB and using files bigger that
two times that size. This benchmark tests used 8 MiB blocks for optimal performance. The previous
performance test section has a more complete explanation for those matters.