Design 64TB MSDP Server

I'm looking for some design specs to help me size the hardware I need for a linux msdp server.  Looking to build a 64TB MSDP pool.

What I know:

1.  IBM 3650 (supports up to 8 or 16 internal drives)

2.  4 x 10Gethernet

3.  4 x 8G FC

4.  RedHat Linux

5.  SAN array to store the backup data

How do I figure out how much disk space I need for the fingerprint DB (metabase).  I'm not finding much useful information and I just don't think this should be all that big of a deal.  I'm being told that the fingerprint DB should live on fast disk (15K or SSD) and that it will be anywhere up to 10% of the size of the pool (so 6.4TB!!!).  That makes for a LOT of $$ on 15K or SSD drives...!!!

Any help would be very welcome.

Thanks, Scott