Controller Enclosure can be called as Array Enclosure or Array head or Chassis.
In your case you need to buy both Chassis and Controllers because MSA 2040 Chassis will not support MSA 2050 controllers.
All details covered inside upgrade document,
https://h20195.www2.hpe.com/v2/Getdocument.aspx?docname=a00015116enw
Now coming to your other query, "Are these cables inside the chassis?? Are these necessary for an iSCSI SAN?? "If you are moving to MSA 2050/2052 SAS controllers, you will need to purchase cables with HD mini-SAS (SFF 8644 connector) connectors for connection to the MSA 2050/2052 SAS host ports."
Ans: This is not applicable for your case as this is applicable if you want to move to SAS interface. Your requirement is iSCSI which is different protocol than SAS
Hope this helps!
Regards
Subhajit
I am an HPE employee
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