EMC VNXe configuration NL-SAS hard disk number mandatory must be a multiple of 6

Symptom:
VNXe3150 storage one, configured as six NL-SAS 2T hard drives. During the use process, it was found that there was not enough space and needed to be expanded. I expected to purchase four NL-SAS 2T hard drives of the same model to form raid5, but I have been unable to find the four new hard drives.
Cause analysis:
The biggest feature of this product configuration is its raid mode. The relatively straightforward description is: the system has solidified the raid mode of its hard disk, it will automatically identify the model and number of the hard disk, and automatically and compulsory use of the fixed raid division. Please refer to the following form for details:

Solution:
Check the relevant documents and confirm. In this NL-SAS hard disk, the system will force the Raid 6 (4+2) mode, so only 4 expansion disks do not meet the number of hard disks. After adding two hard disks of the same model, the system immediately recognized the newly added 6 hard disks and also smoothly divided the space according to the Raid 6 (4+2) mode.
Remarks:
EMC VNXe configuration NL-SAS hard disk number mandatory requirements must be a multiple of 6, otherwise it can not be used.