The members do not need to be the same size for a concatenated meta, AFAIK, but it is probably not a bad thing to keep them the same size.  Not sure what the performance requirements for this 7TB volume is, as a striped meta may offer more performance.  You can add FAs instead of striping and get more performance as well.
Hi All ,      I'm new to vmax and still learning , need your expertise please  , we have a request to expand a metalun . My plan is as below , let me know if Im doing it right , I cant seem to find any docs reg best practises for metaluns on vmax .   Vmax 20 K - 5876 . SE -- 7.2.1.0 Concatenated : Metalun currently at  ---- 3TB= 16 TDEVS X 192000 MB  To be expand by creating -- 4TBI  ~ 22TDEVS X 192000 MB  ..  Im planning to create 22 TDEVS of 192000 MB each and add these to the metahead . . Is this approach good? What other ways can I expand this other than migration .   All meta members should be at the same size  for concatenatenation ? What points to I have to keep in mind before i perform any meta expansion (other than size ) .  Peace !
Vmax - Expanding MetaLun 3 TB to a 7 TB