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Remember to set the scheduler to cfq on the SR, and to ensure that the PBD has been re-plugged in order
for the scheduler change to take effect.
The first parameter is qos_algorithm_type. This parameter needs to be set to the value ionice, which
is the only type of QoS algorithm supported for virtual disks in this release.
The QoS parameters themselves are set with key/value pairs assigned to the qos_algorithm_param
parameter. For virtual disks, qos_algorithm_param takes a sched key, and depending on the value, also
requires a class key.
Possible values of qos_algorithm_param:sched are:
•sched=rt or sched=real-time sets the QoS scheduling parameter to real time priority, which requires
a class parameter to set a value
•sched=idle sets the QoS scheduling parameter to idle priority, which requires no class parameter to
set any value
•sched=<anything> sets the QoS scheduling parameter to best effort priority, which requires a class
parameter to set a value
The possible values for class are:
• One of the following keywords: highest, high, normal, low, lowest
• an integer between 0 and 7, where 7 is the highest priority and 0 is the lowest, so that, for example, I/O
requests with a priority of 5, will be given priority over I/O requests with a priority of 2.
To enable the disk QoS settings, you also need to set the other-config:scheduler to cfq and replug
PBDs for the storage in question.
For example, the following CLI commands set the virtual disk's VBD to use real time priority 5:
xe vbd-param-set uuid=<vbd_uuid> qos_algorithm_type=ionice
xe vbd-param-set uuid=<vbd_uuid> qos_algorithm_params:sched=rt
xe vbd-param-set uuid=<vbd_uuid> qos_algorithm_params:class=5
xe sr-param-set uuid=<sr_uuid> other-config:scheduler=cfq
xe pbd-plug uuid=<pbd_uuid>