Friday, February 19, 2010

XenServer - Disk Access Priority (qos)

Following are steps for setting Disk Access Priority in XenServer 5.5

Note: I found that the Admin Guide and Technote provided by Citrix for making these changes have typos in the commands. This could cause unexpected results and more obviously Disk Priority doesn't work (most notible by the slider not working).

Note the message that is displayed briefly when hovering over the slider "This feature is disabled due to license restrictions on the server" has nothing to do with license restrictions, but rather just that it needs enabled on the SR.

  • Shutdown all vm's on the SR
  • xe sr-list name-label="srname" (this will give you the SR UUID)
  • xe sr-param-set uuid=UUIDofSR other-config:scheduler=cfq
  • Detach and reattach the SR (or uplug and replug each pbd for the SR, detach reattach effectively does this)
  • Change the slider to the desired setting

If you happened to follow the admin guide or technotes and used the incorrect command (xe sr-param-set uuid=uuidofsr other-config:scheduler-cfq, note the -cfq rather than =cfq) then you will need to clear this setting first.

xe sr-param-clear uuid=sruuid param-name=other-config

Technote - Correct

Technote - Incorrect

Admin Guide - Incorrect

Bug #2

The Disk Access Priority level (highest / lowest) is displayed incorrectly at 0 and 7 settings. They infact show opposite of what they should. (0 = lowest, 7 = higher). This only shows on the VM storage tab. Setting of 8 shows normal. This can be ignored as a GUI / display bug, go by the numbers. 0 - 7 (according to Admin Guide) with 7 having more priority over 0. Unsure if 8 is valid or not although it can be selected.

Should be High

Should be low