We're considering hardware changes and wondered about the option of a HSN for now but converting it to active in the future when we need more active capacity. I understand that if we did that, we'd be sacrificing full performance continuity and accepting degraded performance continuity. Regardless, our sales team reports that it's not even possible to make the conversion, to take an HSN and make it active. Has anyone had experience converting an HSN to active?
I raised the similar thing to Teradata. We were having 2+1 5500H nodes. Due to IO boundness, I thought of bringing the HSN into configuration. But Teradata was totally against it. The things that you need to know before doing such things is if the storage array cabinet can support that. If it is fine then you need to buy the license from Teradata for that extra node (which is generally huge, in terms of money).
Isn't the intended purpose of a HSN for high availability only? It is not intended to behave like a mainframe where you can "purchase" additional MIPS periodically to help you deal with a performance bottleneck or temporary increase in your workload.
However, I do remember reading something (that may be announced at Partner's this year) about Teradata offering capacity on demand solutions in the near future. These systems may not have been reached general availability yet so details may be sketchy.
In the meant time, your capacity planning for new hardware should take into account expected growth for the duration of your lease or amortization of the new hardware. I'm sure Teradata sales or PS can assist you (or provide you materials) in this planning if this is your first time going through the process.