First of all, thank you so much for your valuable time.
It probably does, though we have a requirement of having available at least twice the expected database size, and 50% of disk space overhead sounds like too much for us to take in a replicated SAN environment and a PostgreSQL master/slave - streaming replication setup.
our options regarding disks availability at the moment are:
a 3 disks array dedicated for PostgreSQL in any RAID configuration we'd like
OR
a 10 disks array shared with 14 virtual machines running the middleware layer and the application infrastructure in a RAID 5 configuration
again, I do really appreciate your kindly help.