Re: Configuring new member in existing Group
Pro: They would work together on all volumes in that pool. All volumes by default spread across both members. The amount is proportional to how big each one is in comparison to the other. So if one is twice as big, it will hold 2/3 of the data for each volume.
Con: If one member fails, all volumes they have in common will be offline until the problem is resolved
The particular 'con' is your case is the Hybrid array. It's faster but to complete each server IO, both will have to process their share of the data. The hybrid will do it faster of course. But server won't see that until the NL-SAS member finishes.
If that slower member gets behind it will move busy pages to the hybrid for idle pages on the hybrid.
Given the expense of the hybrid, and usually bought for specific role. SQL, VDI, Exchange it's best to put it in its own pool. At least to start. You can move volumes from the NL-SAS array to the hybrid at any time, live.
If you have SANHQ you can see what your current load and IO patterns are and help move volumes needing the lowest possible latency to the Hybrid. This also improves the NL-SAS array's performance too.
Later you can always merge them. That's easy. Going other way is long and time consuming assuming you have the free space to do it later.
Hopefully, that helps?