Administrator Guide

Performance characterization
45 Dell EMC Ready Solution for HPC PixStor Storage | Document ID
(odd numbered clients to first gateway and even numbered clients to the second gateway). This manual
configuration was used to deterministically have half of the clients mounted from each Gateway.
Sequential IOzone Performance N clients to N files
Sequential N clients to N files performance was measured with IOzone version 3.487. Tests executed varied
from single thread up to 512 threads in increments of powers of two (since there are not enough cores on the
clients for executing efficiently 1024 threads).
Caching effects on the servers were minimized by setting the GPFS page pool tunable to 16GiB and using
files bigger than two times that size. It is important to notice that for GPFS that tunable sets the maximum
amount of memory used for caching data, regardless the amount of RAM installed and free.
To avoid any possible data caching effects from the clients, the total data size of the files was twice the total
amount of RAM in the clients used. That is, since each client was considered as having 256 GiB of RAM, for
threads counts equal or above 16 threads the file size was 8192 GiB divided by the number of threads (the
variable $Size below was used to manage that value). For those cases with less than 16 threads (which
implies each thread was running on a different client), the file size was fixed at twice the amount of memory
per client, or 512 GiB.
Even that for the solution native client, the optimum block transfer size is 8 MiB, for consistency with
benchmarks executed on NFS, the block size for large sequential transfers was set to 1 MiB, since Samba
has smaller maximum transfer sizes.
The following commands were used to execute the benchmark for writes and reads, where $Threads was the
variable with the number of threads used (1 to 512 incremented in powers of two), and threadlist was the file
that allocated each thread on a different node, using round robin to spread them homogeneously across the
16 compute nodes.
./iozone -i0 -c -e -w -r 1M -s ${Size}G -t $Threads -+n -+m ./threadlist
./iozone -i1 -c -e -w -r 1M -s ${Size}G -t $Threads -+n -+m ./threadlist