HP 3PAR OS 3.1.3 CLI Administrator's Manual

contains one or more VVs that make up a datastore, controls the I/O across all VMs using that
datastore. This could be suboptimal, however, as some VMs need more I/O resources than others.
Combining QoS with SIOC offers I/O control up to the level of an individual VM—an I/O share
and an optional IOPS limit defined per VM distribute the available I/O capacity in a fair way
across VMs, ensuring that no single VM consumes all the I/O provided to the VVset through QoS
settings. Note that SIOC will not respond to queue-full messages from QoS directly.
HP 3PAR Priority Optimization can also cooperate with AQD to manage I/O. AQD handles I/O
congestion in the I/O path to the datastore LUN. It does so by halving the queue length to the LUN
when a queue-full message arrives at the ESXi host. This reduction in the queue length gives the
array an opportunity to decrease the number of outstanding I/Os at its end. In vSphere 5.1 U1,
AQD can be configured by LUN, or globally for the ESXi host.
Combining QoS rules with SIOC and ADQ provides I/O congestion control on three different
levels: the workload will honor the QoS limits, and it will be impacted indirectly when SIOC reacts
to latency increases and when AQD responds to queue-full messages from QoS rules. Coordination
and some experimenting may be necessary to deliver the best results.
VMware Storage DRS, a new feature introduced in VMware vSphere 5.0, groups datastores into
a cluster so that they are managed as a single unit. This allows for load balancing VMs across
datastores based on I/O latency and space utilization in an automated or manual way. Storage
DRS leans on Storage vMotion for migrating VMDKs to different datastores. Combining HP 3PAR
Priority Optimization with Storage DRS requires careful planning of the QoS rules. A QoS rule
governs one or more LUNs that make up a datastore. Storage DRS implies a source and a
destination datastore, each possibly subject to a QoS rule. The QoS rule if any on the Storage
DRS destination datastore should have enough headroom to accommodate the additional I/O
capacity of the migrated VMDK. If the workload’s I/O characteristics are not very well known, HP
recommends manual Storage DRS migrations over automated ones to detect any I/O congestion
due to the migration in an early stage.
Reporting
Continuous performance monitoring of all critical parameters of a storage system is essential in
managing a storage system. HP 3PAR Priority Optimization features new charts in the HP 3PAR
MC for monitoring QoS rules graphically over time.
Use the HP 3PAR CLI command statqos to display run-time statistics of active QoS rules in
columns. The command produces output every 2 seconds; this interval can be changed. Depending
on the active QoS rule, values for the following parameters are displayed:
• IOPS
• Bandwidth
• Service time (Svt_ms)
• Wait time (Wtt_ms)
• Size of the I/O requests (IOSz_KB)
• Accumulated number of rejected I/O requests (Rej)
• Instantaneous averaged QoS queue length (Qlen)
• Instantaneous averaged wait queue length (WQlen)
The column headers show:
Type QoS target type (vvset or sys)
Name QoS target name; also the name of the VVset on which the rule is
defined
I/O_per_second IOPS cap, set by the userQt
Cur Current IOPS
Using HP 3PAR Priority Optimization 159