Why not add disk / memory when low on resources?

Hi,

It might be stupid query but let me ask.

Suppose I have decided to go for HANA with 1 TB size in memory. So disk space will be 4 TB.

Now suppose we came to know in later stage that 1 TB memory in not sufficient and we should add more memory.

Now my query is

1. Can we just extend more memory just like we do on normal [ Non HANA ] system.

    Can we do it or not ? If not why?

2. If 1 is not the solution , I think scale out the another solution. So slave nodes have to be HANA Appliance?

Regards,

Vinay