Machines: Proliant ML 350 G5 with raid controller.
for my enterprise I have to install/configure following Linux based Servers
1, Mail Server(Postfix)
2, Web-proxy Server(Squid)
3, NFS FileServer(users home directory)

please suggest me the best hware based RAID-level(1 or 5) and filesystem(ext3, reiserfs, or xfs) for the
a, user's mailboxes (/var/spool/mail)
b, squid's cache_dir
c, /home

I have the following plan

volume for the Linux OS of either Server(1, 2 or 3) will be raid-1
Linux OS ''/": /dev/sda1, /dev/sdb1, /dev/sdc1
here /dev/sdc1 is spare

volume for the users mailboxes /var/spool/mail, Squid's cache_dir, and user's home directory /home will also be raid-1: /dev/sdd1, /dev/sde1, /dev/sdf1
here /dev/sdf1 is spare

As my enterprise requires fastest Read/Write operations, and zero downtime, I am opting for raid-1(with spare disk) becuase its comparitively fast(then raid-5).

Please suggest and recommend the best RAID-level for the above servers.

Also please suggest/recommend the best filesystem(ext3, reiserfs, or xfs) for
/var/spool/mail (user's mailboxes)
/var/squid/cache (squid cache_dir)
/home (NFS based)