Although xtrabackup does not block your database’s operation, any backup
can add load to the system being backed up. On systems that do not have much
spare I/O capacity, it might be helpful to throttle the rate at which
xtrabackup reads and writes data. You can do this with the
xtrabackup --throttle option, this option limits the number of I/O
operations per second in 1 MB units.
Image below shows how throttling works when
xtrabackup --throttle is
When specified with the
xtrabackup --backup option, this option
limits the number of pairs of read-and-write operations per second that
xtrabackup will perform. If you are creating an incremental backup, then the
limit is the number of read I/O operations per second.
By default, there is no throttling, and xtrabackup reads and writes data as quickly as it can. If you set too strict of a limit on the I/O operations, the backup might be so slow that it will never catch up with the transaction logs that InnoDB is writing, so the backup might never complete.