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Chapter 7. Block I/O
This chapter covers optimizing I/O settings in virtualized environments.
7.1. Block I/O Tuning
The
virsh blkiotune
command allows administrators to set or display a guest virtual machine's block I/O parameters manually in the <blkio>
element in the guest XML configuration.
To display current
<blkio>
parameters for a virtual machine:
# virsh blkiotune virtual_machine
To set a virtual machine's
<blkio>
parameters, use the virsh blkiotune
command and replace option values according to your environment:
# virsh blkiotune virtual_machine [--weight number] [--device-weights string] [--config] [--live] [--current]
Parameters include:
weight
- The I/O weight, within the range 100 to 1000.Increasing the I/O weight of a device increases its priority for I/O bandwidth, and therefore provides it with more host resources. Similarly, reducing a device’s weight makes it consume less host resources.
device-weights
- A single string listing one or more device/weight pairs, in the format of
. Each weight must be within the range 100-1000, or the value 0 to remove that device from per-device listings. Only the devices listed in the string are modified; any existing per-device weights for other devices remain unchanged./path/to/device
,weight,/path/to/device
,weight config
- Add the
option for changes to take effect at next boot.--config
live
- Add the
option to apply the changes to the running virtual machine.--live
Note
The
option requires the hypervisor to support this action. Not all hypervisors allow live changes of the maximum memory limit.--live
current
- Add the
option to apply the changes to the current virtual machine.--current
For example, the following changes the weight of the
/dev/sda
device in the liftbrul VM to 500.
# virsh blkiotune liftbrul --device-weights /dev/sda, 500
Note
Use the
virsh help blkiotune
command for more information on using the virsh blkiotune
command.