More throtting ability for I/O

Implementing as the patch of innobackup?

> Throttling is indeed a very nice feature to have.
>
> Speaking of which (and speaking about nice ;), would it be possible to have the option to use “ionice -c3″ on linux, to lower I/O priority of the backup process while keeping it able to use resources when there’s resources available (as opposed to a hard IOPS upper bound limit)?
>
> Another throttling ability that would be useful, if Xtrabackup works by copying files and plans to have the option to make use of rsync, would be to expose the “–bwlimit” rsync option to end user. That would help to prevent saturating block or network bandwidth.