It seeks to increase the parallelism.
Check the properties of the group has Savegrp parallelism >= 10.
Verify if your pool and device allow writing in parallel.
Create many copies of client SQL within same group, but each client with different SQL data bases, 30 DBs for client is good idea,as Hrvoje Crvelin says.
Please review this links:
30 DBs per client? I have 4 affected servers with a combined total of just under 1000 databases. I would have to manually create a total of 34 clients to back these up. I was hoping for a less labor-intensive solution. If there's a way to create clients from, say, PowerShell, then I could do that and automate the process.
The group parallelism isn't set (== 0, default to client parallelism), but I can test that parameter and see if it helps, too.