Citrix Systems 5.6 manual Virtual disk QoS settings, Adjusting the disk IO scheduler

1.Shutdown the VM.

2.Use the xe CLI to identify the UUIDs of the VDIs to be moved. If the VM has a DVD drive its vdi-uuidwill be listed as <not in database> and can be ignored.

xe vbd-list vm-uuid=<valid_vm_uuid>

Note:

The vbd-listcommand displays both the VBD and VDI UUIDs. Be sure to record the VDI UUIDs rather than the VBD UUIDs.

3.In XenCenter select the VM's Storage tab. For each VDI to be moved, select the VDI and click the Detach button. This step can also be done using the vbd-destroycommand.

Note:

If you use the vbd-destroycommand to detach the VDI UUIDs, be sure to first check if the VBD has the parameter other-config:ownerset to true. If so, set it to false. Issuing the vbd-destroycommand with other-config:owner=truewill also destroy the associated VDI.

4.Use the vdi-copycommand to copy each of the VM's VDIs to be moved to the desired SR. xe vdi-copy uuid=<valid_vdi_uuid> sr-uuid=<valid_sr_uuid>

5.Within XenCenter select the VM's Storage tab. Click the Attach button and select the VDIs from the new SR. This step can also be done use the vbd-createcommand.

6.To delete the original VDIs, within XenCenter select the Storage tab of the original SR. The original VDIs will be listed with an empty value for the VM field and can be deleted with the Delete button.

Adjusting the disk IO scheduler

For general performance, the default disk scheduler noop is applied on all new SR types. The noop scheduler provides the fairest performance for competing VMs accessing the same device. To apply disk QoS (see the section called “Virtual disk QoS settings”) it is necessary to override the default setting and assign the cfq disk scheduler to the SR. The corresponding PBD must be unplugged and re-plugged for the scheduler parameter to take effect. The disk scheduler can be adjusted using the following command:

xe sr-param-set other-config:scheduler=noopcfqanticipatorydeadline \

uuid=<valid_sr_uuid>

Note:

This will not effect EqualLogic, NetApp or NFS storage.

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:

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