Limit Bandwidth of Volume Copy¶
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This proposes adding a new config to limit bandwidth for volume copy to mitigate interference to other instance performance during:
new volume creation from a image
volume deletion (when dd if=/dev/zero etc. is chosen to wipe)
Currently, volume copy operations consumes disk I/O bandwidth heavily and may slow down the other guest instances.
“ionice” option is already implemented in some cases, but it is not always usable. e.g. When instances directly access to the storage and doesn’t go through I/O scheduler of cinder control node, ionice cannot control I/O priority and instances access may slow down.
A new config named ‘volume_copy_bps_limit’ will be added to determine max bandwidth (byte per second) consumed by volume copy.
When CONF.volume_copy_bps_limit is zero (default), no limitation is applied, and no cgroup is created.
Otherwise, bandwidth limitation is applied to volume copy. For example, if the volume copy is done by ‘dd’ command, it can be implemented by putting ‘dd’ into blkio cgroup for throttling.
When volume copy commands have an option for I/O throttling, the usage of such options are preferable. Putting whole cinder-volume processes into blkio cgroups could also be a solution for this, though it is required to provide a way to set rate limit to newly added block devices when new volume is created.
Data model impact¶
REST API impact¶
Other end user impact¶
When volume copy I/O bandwidth is limited, it takes more time to complete volume copy. Users are required to balance between volume copy performance and interference to instances performance.
Other deployer impact¶
This feature is disabled by default. Users who want to use this feature need to set ‘volume_copy_bps_limit’ in cinder.conf.
- Primary assignee:
Implement cgroup blkio setup functions
Implement I/O rate limit for volume_utils.copy_volume
Implement I/O rate limit for other image format such as qcow
The cinder client documentation will need to be updated to reflect the new config.