qemu/docs/throttle.txt

12 I/O operations. The code itself is generic and independent of the I/O
14 and operations per second (IOPS) when performing disk I/O.
20 Using throttling to limit disk I/O
22 Two aspects of the disk I/O can be limited: the number of bytes per
27 I/O limits can be set using the throttling.* parameters of -drive, or
71 I/O bursts
74 user to do bursts of I/O for a configurable amount of time. A burst is
75 an amount of I/O that can exceed the basic limit. Bursts are useful to
81 I/O they allow. These two can be configured separately for each one of
85 The I/O limit during bursts is set using 'iops-total-max', and the
112 With this, the user can perform I/O on hd0.qcow2 at a rate of 2000
116 long period of time with unused I/O (see below for details).
142 Controlling the size of I/O operations
144 When applying IOPS limits all I/O operations are treated equally
146 of this in order to circumvent the limits and submit one huge I/O
150 from happening. This setting specifies the size (in bytes) of an I/O
163 Applying I/O limits to groups of disks
165 In all the examples so far we have seen how to apply limits to the I/O
169 The way it works is that each drive with I/O limits is assigned to a
175 document apply to the combined I/O of all members of a group.
191 I/O requests on several drives of the same group they will be
194 When I/O limits are applied to an existing drive using the QMP command
198    - I/O limits are shared within the same group, so new values will
212    - I/O limits can be disabled by setting all of them to 0. In this
220 I/O limits in QEMU are implemented using the leaky bucket algorithm
224 constantly. The water that gets into the bucket represents the I/O
225 that has been performed, and no more I/O is allowed once the bucket is
245 we can only add as much water as it leaks, therefore the I/O rate is
252 6000, allowing for 3 more seconds of I/O at 2000 IOPS.
255 a lower I/O rate, e.g. 1000 IOPS during 120 seconds.
260 Since QEMU 2.11 it is possible to configure the I/O limits using a
266 them must be assigned to a group that contains the actual I/O limits.
268 described earlier in "Applying I/O limits to groups of disks".
331 that we have three different drives and we want to set I/O limits for
332 each one of them and an additional set of limits for the combined I/O
358 and 3000 respectively but the total combined I/O can never exceed 4000