Actually, the bay 4 is the system.
The bay 1 is the Time Machine... ( 1gb )
When upgrade, the Time Machine will be in the bay 3
And the bay 1 and 2 for a software raid( I will see the size depending of the backup ). So I will need another backup system...
Another array in the same server don't sound good... In case of motherboard injury... The two arrays are lost.