I/O priorities

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Revision as of 20:35, 7 December 2012 by 66.45.235.121 (talk)
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The I/O priorities feature is implemented in OpenVZ since kernel 2.6.18-028stable021, vzctl 3.0.16. This feature allows to assign I/O priority to any container. Priority range is 0-7. 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 4. Examples of using:

vzctl set 101 --ioprio 0 --save
vzctl set 101 --ioprio 7 --save

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 0 prio corresponds to time slice t, than 8 prio corresponds to time slice 2 * t. Default time slice value is HZ/2. The main criteria for fairness at the moment is that if you set I/O prio of CT 1 to p1 and I/O prio of CT 2 to p2, and p1 > p2 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