Administrator Guide

Performance characterization
24 Dell EMC Ready Solution for HPC PixStor Storage | Document ID
Metadata performance with MDtest using empty files
Metadata performance was measured with MDtest 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 512 threads. The
benchmark was used for files only (no directories metadata), getting the number of creates, stats, reads and
removes the solution can handle.
To properly evaluate the solution in comparison to other DellEMC HPC storage solutions, the optional High
Demand Metadata Module was used, but with a single ME4024 array, even that the large configuration and
tested in this work was designated to have two ME4024s.
This High Demand Metadata Module can support up to four ME4024 arrays, and it is suggested to increase
the number of ME4024 arrays to 4, before adding another metadata module. Additional ME4024 arrays are
expected to increase the Metadata performance linearly with each additional array, except maybe for Stat
operations (and Reads for empty files), since the numbers are very high, at some point the CPUs will become
a bottleneck and performance will not continue to increase linearly.
The following command was used to execute the benchmark, where Threads was the variable with the
number of threads used (1 to 512 incremented in powers of two), and my_hosts.$Threads is the
corresponding file that allocated each thread on a different node, using round robin to spread them
homogeneously across the 16 compute nodes. Similar to the Random IO benchmark, the maximum number
of threads was limited to 512, since there are not enough cores for 1024 threads and context switching would
affect the results, reporting a number lower than the real performance of the solution.
mpirun --allow-run-as-root -np $Threads --hostfile my_hosts.$Threads --prefix
/mmfs1/perftest/ompi --mca btl_openib_allow_ib 1
/mmfs1/perftest/lanl_ior/bin/mdtest -v -d /mmfs1/perftest/ -i 1 -b $Directories
-z 1 -L -I 1024 -y -u -t -F
Since performance results can be affected by the total number of IOPs, the number of files per directory and
the number of threads, it was decided to keep fixed the total number of files to 2 MiB files (2^21 = 2097152),
the number of files per directory fixed at 1024, and the number of directories varied as the number of threads
changed as shown in Table 4.
Table 4 MDtest distribution of files on directories
Number of Threads
Number of directories per thread
Total number of files
1
2048
2,097,152
2
1024
2,097,152
4
512
2,097,152
8
256
2,097,152
16
128
2,097,152
32
64
2,097,152
64
32
2,097,152
128
16
2,097,152
256
8
2,097,152
512
4
2,097,152
1024
2
2,097,152