Citrix Systems Understanding Citrix QoS Settings for Virtual Disks and Performance Management

2.This command suspends the VM (unless it is already powered down), initiates the space reclamation process, and then resumes the VM.

Note:

Citrix recommends that, before executing the off-line coalesce tool, you shutdown or suspend the VM manually (using either XenCenter or the XenServer CLI). If you execute the coalesce tool on a VM that is running, the tool automatically suspends the VM, performs the required VDI coalesce operation(s), and resumes the VM.

If the Virtual Disk Images (VDIs) to be coalesced are on shared storage, you must execute the off-line coalesce tool on the pool master.

If the VDIs to be coalesced are on local storage, you must execute the off-line coalesce tool on the server to which the local storage is attached.

Virtual Disk QoS Settings

Virtual disks have an optional I/O priority Quality of Service (QoS) setting. This setting can be applied to existing virtual disks using the xe CLI as described in this section.

In the shared SR case, where multiple hosts are accessing the same LUN, the QoS setting is applied to VBDs accessing the LUN from the same host. QoS is not applied across hosts in the pool.

Before configuring any QoS parameters for a VBD, ensure that the disk scheduler for the SR has been set appropriately. See the section called “Adjusting the Disk IO Scheduler” for details on how to adjust the scheduler. The scheduler parameter must be set to cfq on the SR for which the QoS is desired.

Note:

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-timesets 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:schedulerto 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:

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