HP 3PAR Command Line Interface Administrator's Manual: HP 3PAR OS 3.1.2 (QR482-96525, September 2013)

NOTE: Queue depth is the average number of I/O jobs, either processing or waiting to be
processed, within a polling interval. The queue depth is a non-negative integer number.
• When upgrading the end-to-end SAN pathing from 4 Gb/sec to 8 Gb/sec.
In general, HP recommends review of the system I/O capability and adjustment of the QoS rules
in use whenever a change was made to one part of the entire chain from the host to the HP 3PAR
OS.
Handling Tier-1 Applications
The HP 3PAR StoreServ storage systems are Tier-1 arrays that can handle multiple mission-critical
workloads concurrently, as opposed to workloads of medium importance and performance
requirements. Tier-1 applications should be given all resources they need during runtime, given
their vital business impact.
HP recommends that a QoS rule be defined with sensible limits for IOPS and bandwidth on all
VVsets that have a known I/O profile. The System rule should be defined to control all volumes
created on the system that do not have an explicitly defined QoS rule.
If you don’t set a QoS rule, and the all_others rule is active, mission-critical applications will
be subject to the all_others rule. To prevent the System rule from controlling the Tier-1
applications, define a QoS rule with very high values for IOPS and bandwidth. This way, the
mission-critical workload will be able to consume the I/O resources they need to perform optimally.
Implementing the System Rule
Workloads without a QoS rule consume I/O resources in an uncontrolled manner and may starve
those that are subject to a QoS rule. To ensure an acceptable level of performance across all
applications on a storage system if QoS is used, all volumes must be part of a QoS rule with
meaningful limits reflecting the application’s I/O requirements. The System QoS rule should be
enabled and a value specified for its maximum IOPS and bandwidth to control the I/O traffic from
VVs and VVsets not subject to a specific QoS rule. This prevents any new volumes added to the
HP 3PAR StoreServ or existing ones that are not subject to a QoS rule from negatively affecting
the entire system overconsuming IOPS or bandwidth.
As explained in “Creating a New QoS Rule with the HP 3PAR MC” (page 155), the default minimum
allowed values for the System rule are 1000 for the I/O Limit and 100,000 KB/sec for the
bandwidth limit. Be sure to change these to acceptable values if the defaults are deemed too small.
Overprovisioning the System
HP 3PAR Priority Optimization allows over-provisioning when creating QoS rules: rules whose
combined value for IOPS or bandwidth can exceed the I/O capacity of an HP 3PAR StoreServ.
This is an established practice if the workloads are sufficiently orthogonal in their I/O usage.
For example, a database used only during the day time and a backup application running only
during the night can each be given the entire I/O capacity of the system in their respective QoS
rules. When overprovisioning concurrent workloads, QoS prevents a single application or customer
from monopolizing the system.
For another example, a system capable of 50 k IOPS could have 10 customers, each limited to
10 k IOPS. The system is over-provisioned for IOPS, but no single customer can monopolize the
system. Continuous monitoring of system performance by HP 3PAR System Reporter is mandatory
to ensure that every application and customer performs well without reaching their I/O limits.
QoS Influence on the Host Side
The QoS rules in HP 3PAR Priority Optimization specify the relative importance of the I/O of each
workload on the storage system. When the IOPS or bandwidth demand of an application reaches
the implemented QoS limits, the performance of the application on the host will no longer grow.
Using HP 3PAR Priority Optimization 161