Hi,

first of all - that's no problem. You should start both storeBackup.pl's directly in parallel, because then filesystem caching will be perfect and the two backups will take about the same time than one backup. (This is not true if you have really lots of new files to compress and if you have slow cpus.)

In detail:

1. It's a very bad idea to run the_same_backup into the same backupDir multiple times. The result would be not hard linked new files in each backup with no additional advantage.

2. Say you run two different backups into the same backupDir at the same time (different series). If these two backups have no identical files, the result will be the same as running one after the other. In this case, you should set option otherBackupSeries so storeBackup.pl does not waste time reading the md5 sums of the other backup.

3. You run two different backups into the same backupDir at the same time (different series) but have identical files in the backup. This might happen if two people with laptops (and shared files) make independent backups. In this case, the identical new (!) files will not be hard linked. However, starting with the next backup, each of these two different series will hard link against the_same inode in the backup (backupDir). So after some time, the "lonely" hardlink will be removed by deletion of old backups.
If the backups were run sequentially, the new identical files from the different series will be hard linked normally (as long as you do not define something different with option otherBackupSeries).

Also a long answer ;-)

Does it answer your question?

Regards, Heinz-Josef