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The I/O priorities feature is implemented in OpenVZ since kernel <tt>2.6.18-028stable021</tt> kernel and since , <tt>vzctl 3.0.16</tt>. This feature allows to assign I/O priority to any [[VE]]. Priority range is <tt>0-7</tt>. The more priority a [[VE]] has, the more time for using block devices this [[VE]] will obtain. Note, that this feature is implemented on base of 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:
<pre>
vzctl set 101 --ioprio 0 --save
</pre>
The mapping from priority to time is the following: if <tt>0</tt> prio corresponds time slice <tt>t</tt>, than <tt>8</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 VE 1 to <tt>p1</tt> and I/O prio of VE 2 to <tt>p2</tt>, and <tt>p1 > p2</tt> then VE 1 should do more I/O than VE 2.
[[Category: Resource management]]
