XtraBackup is an Open Source online (non-blockable) backup solution for the InnoDB and XtraDB storage engines. It works with both MySQL 5.0 and 5.1 (and possibly 5.4 as well) and is distributed under the GPLv2.
Some weeks ago Vadim announced the availability of xtrabackup-0.7, stating that they consider it stable enough now to label this version a "Release Candidate". I've been maintaining RPM packages of xtrabackup on the fine openSUSE Build Service for quite some time now, RPMs of 0.7 for a number of distributions are now available for download. Please report any bug reports via the bug tracker on Launchpad.
