Is it one client we're talking about, or four?
If it's only one, you could do a script like this:
load dsmc arc /dir1/.../*
load dsmc arc /dir2/.../*
load dsmc arc /dir3/.../*
load dsmc arc /dir4/.../*
In this way, each command is executed, and when the first is finished, the second will start and so on.
If its four server, I would guess you have to split up the archive schedule with a large amount of time between the schedules.
Best Regards
Daniel Sparrman