Developers Guide

Performance considerations
45 Dell EMC SC Series with Red Hat Enterprise Linux 7x | CML1071
4.1 Tuning profiles
RHEL 7.x introduced a new set of tools to assist administrators and storage professionals with tuning RHEL
hosts. This is achieved using two new commands, tuned and tuned-adm, which manage a set of predefined,
performance-tuned profiles. The following output presents the active tuning profile (default) as well as the list
of alternative tuning profiles that can be applied. It is recommended to use the default tuning profile,
throughput-performance, with any SC Series storage implementation. The discussion of each tuning profile
and its merits are outside the scope of this paper, however further discussion of this topic can be found in
online Red Hat documentation.
# tuned-adm active
Current active profile: throughput-performance
# tuned-adm list
Available profiles:
- balanced
- desktop
- latency-performance
- network-latency
- network-throughput
- powersave
- sap
- throughput-performance
- virtual-guest
- virtual-host
4.2 Using multiple volumes
A volume is only active on one SC Series controller at any one time. Therefore, where possible, distribute
volume workload evenly across both SC Series storage controllers to most effectively leverage simultaneous
I/O processing. A larger number of smaller-sized volumes will often result in better performance than fewer
larger-sized volumes. From a Linux perspective, having multiple target volumes can result in performance
improvements by leveraging the kernel to process I/O in parallel to addressing multiple paths and SCSI
devices.
In SAS-connected environments, paths from both controllers are presented to the connected host
(active/optimized and standby), however only the active/optimized path is used for all active I/O at any one
time. When the active/optimized path becomes unavailable, the SC Series array will dynamically determine
which one of the remaining standby paths will assume the role of the active/optimized path and continue to
stream active I/O to the new active/optimized path. This is accomplished by explicitly pinning volumes to a
different controller when mapping these volumes to the server object. This feature is accessible using the
Advanced Options on the mapping dialog shown as follows.