12 disks raid setup

Hi,

I am in the process of setting up a postgresql server with 12 SAS disks.

I am considering two options:

1) set up a 12 disks raid 10 array to get maximum raw performance from
the system and put everything on it (it the whole pg cluster, including
WAL, and every tablespcace)

2) set up 3 raid 10 arrays of 4 disks, and dispatch my data on these
disks via tablespaces :

data1 = pg cluster + references data (dimensions) tablespace
data2 = fact data tablespace
data3 = indices tablespace

Typical workload is either massive insert/update via ETL or complex
queries on big (10 millions tuples) tables with several joins (including
Mondrian ROLAP).

Does anyone have an opinion of what could give best results ?

Thanks,
Franck