HPE 4130 upgrade to 8 disks

I am working with a customer who has a SAN cluster with 1 x 4130 (4x600Gb) and 1 x 4330 (8x900Gb) - don't ask!

I am wanting to increase the number of disks in the 4130 to 8x600Gb so that we can increase the available capacity of the cluster.

I have inserted a drive in slot 5, the lights come on, but nothing shows in the CMC.

Is the 4130 limited to 4 disks?

I cannot find information which confirms or denies this - several references to 4 free bays, pictures of units with 8 drives, but also diagrams showing only 4 drives.

Your help would be most appreciated.

Thanks

Martin