TL:DR --> no, for EC4+2/5+2 you need more hosts, no matter number of disks, and tiered EC4+2/5+2 are not generally available as of now to all users.
Long version:
replicas should be considered per NODE, not per DISK.
Will fallback on disks only if no other option is available (but that’s not the way to guarantee data integrity in an hyperconverged system designed as NodeWeaver)
For EC 5+2 you need 7 hosts, not 7 disks:
example: 5 nodes will hold a parity chunk, 2 nodes will hold the full chunk
For EC 5+2 on 4 hosts you won’t have enough resiliency:
example: on 3 nodes you’ll have 2 chunks (or 1 parity chunk + 1 chunk, or 2 parity chunks), and on 1 node you’ll have 1 chunk (1 chunk or 1 parity chunk)
the nodes with 2 chunks will place them on different chunkserver (one on HDD one on SSD ) but that doesn’t matter because, if that node dies, you’ll lose 2 replicas with the death of a single node and therefore 5+2 will do same of 2+2 in a 4 nodes scenario.
It’s just saving you a bit more if a single disks fails, but the price for overhead is not worthy.
That said custom tiering erasure coding are possible, but custom configurations are reserved to clusters with more than 5 nodes opting for 24/7 support and should be requested through ticket, otherwise will have to stick to proposed goal config.
no matter how many drives you have ssd or hdd, a single node exposes 4 types of chunkserver SSD, HDD, SSDCRYPT, HDDCRYPT (all disks fall in the relative media label and have a dynamic encrypted partition available for the encrypted goals).
in theory a tiered 5+2 EC goal may look like this (or similar to this depending on the media placement % balance)
TIER_EC52 TIER_EC52: $ec(5,2) {SSD SSD SSD HDD HDD HDD HDD}
to have a valid goal you still need to have 7 hosts, anything less will be accomplished only in “emergency mode” when strict goal media labels are not respected (this happens when a user fills too much a certain label SSD/HDD, NodeWeaver will automatically start balancing on the others), not by chance is called “emergency mode” : it’s something that should not be performed by default.