I needed to do this for quite some time.  I just recently upgraded from 10 gigs to 24 gigs of ram as my host was running out of ram due to the creeping doom that is modern codebase growth everywhere.  I also have quite a bit of data residing on old hard disks that are approaching 5 years of on-time.  I would rather replace them proactively with larger capacity ones now.  This is going to achieve the following things:

1.  Increase data storage performance due to using higher density hard disks.

2.  Reduce the chance of failure of the primary VM array due to using new hard drives

3.  allows me to utilize the secondary array for all three vm’s using storage spaces and

4.  Allows me to setup the two 500 gigs drives as external backup targets for the altaro backup software

I increase my backup storage pool, increase my performance of my vm arrays(both are raid 1) and decrease age related failures of the primary vm array(the one that contains my OS and the primary vm aka a server 2k8 AD DC).  The secondary array now has faster hdd’s for it’s array as well(this is for my Sophos UTM firewall and the Sophos SUM management server for my Sophos UTM installs).  While not important to me total storage goes waaay up.  The primary array is now doubled to 3TB and the secondary array is now tripled to 1.5TB.  I currently have one external hdd compressed backup of the primary vm and the utm vm and have an uncompressed backup of all three vm’s via hyper-v export to another external hdd.  The 500 gig hdd’s will retain their vm images of the UTM and SUM vm files as well until 30 days of testing has passed.