Changes
Corrected a mispelling error, but still there is an important question unanswered, what is HZ?
The I/O priorities feature is implemented in OpenVZ since kernel <tt>2.6.18-028stable021028stab021</tt>, <tt>vzctl 3.0.16</tt>. This feature allows to assign I/O priority to any [[container]]. Priority range is <tt>0-7</tt>. The more priority a container has, the more time for using block devices this container will obtain. This feature is based on CFQ I/O scheduler, so this scheduler should be used for block device in question. Default I/O priority is <tt>4</tt>. Examples of using:
== Examples ==
Set the lowest priority:
vzctl set 101 --ioprio 0 --save
Set the highest priority:
vzctl set 101 --ioprio 7 --save
== Details ==
The higher the value you use, the more I/O time your container will receive.
The mapping from priority to time is the following: if <tt>0</tt> prio corresponds to time slice <tt>t</tt>, than then <tt>87</tt> prio corresponds to time slice <tt>2 * t</tt>. Default time slice value is <tt>HZ/2</tt>. The main criteria for fairness at the moment is that if you set I/O prio of CT 1 to <tt>p1</tt> and I/O prio of CT 2 to <tt>p2</tt>, and <tt>p1 > p2</tt> then CT 1 should do more I/O than CT 2. In simple form the priorities are relative with the higher priority getting more I/O time.
== See also ==
* [[I/O limits]]
* [[IO accounting]]
[[Category: Resource management]]
[[Category: HOWTO]]
