I have two clients who are using TurboStore 7x24 True Online Backup.
Each of them has three HP3000's and all of the machines are on MPE/iX 5.5.
There was a bug last winter, which was fixed by a patch around six months
ago, and since then there haven't been any problems.
It's a good idea to start the backup at a point of low activity, because it
does
have an impact on response time when the machine gets busy.
Cecile Chi