Comment 1 for bug 1086286

Yes, it's necessary for XtraBackup to detect existing backup, and maybe a "lock" file is more accurate for this situation.

For our environment, there are many MySQL instances and we backup daily. Some instances are too huge to finish backup in 24h, so there maybe two running backup processes, and this will failing backup, for example the 'xtrabackup_suspended_2' file of this first run backup was removed by the second.

And the lock file should be specific to one instance, such as put in backup tmpdir or take a name unique to an instance(ip+port), cause there could be more than one mysqld instance in a host.