here's the situation. i have an F330, currently with 20 4Gb discs in three shelves. it is not performance-bound, it's capacity-bound. i'd heard (from netapp) sometime back that, at some future date, mixed 4 and 9 arrays would be permitted, but that i couldn't remove existing 4s, and that 9s would require a dedicated shelf. therefore, i'd tried to keep my disc load on three shelves, and so far succeeded.
if i understand correctly, whilst i will shortly be allowed to mix 4s and 9s, i won't be allowed to use a full set of 9s - in fact, i'll be limited to 21*4 + 3*9 for data, with one hot spare and one parity, leaving me two disc slots i can't use.
is this in fact the case, and if so, would anyone care to try to explain why, *bearing in mind that this toaster is definitely not performance-limited*?
Do you know if the mixed-shelf config has been announced? The person you spoke with may have just been speculating, rather than actually promising anything...
In any case, the reason is that the F330 is limited in the maximum filesystem size it can have (117GB). Not sure if the reasons are entirely technical or marketing driven, but clearly one can see the desire of a company to differentiate a product line by capacity, even if you could *theoretically* get more capacity. One could ask a similar question - why not 3 SCSI cards? The slots are there... but for whatever reason, Network Appliance has chosen not to offer/support that configuration on an F330. There are other customer considerations in general that also might not relate to your specific case, such as the amount of time to do a backup and restore, reconstruction time, etc.
I have the same sort of issue at times... there are cases where I need a lot of online storage, but I don't really need a 500 MHz alpha CPU to handle the load. This type of storage may almost be archival in nature, and thus perhaps a nearline or HSM solution would be more appropriate for the data.
Bruce