Network also matters. It would take a lot of time sending 6TB over 1Gb link, even fully saturating it. IMHO You can try with 10Gb, but you will need to raise your streaming/compaction limits a lot.
Also you will need to ensure that your compaction can keep up. It is often done in one thread and I am not sure if it will be enough for you. As of parallel compaction, I don't know exact limitations and if it will be working in your case.

2012/9/18 Casey Deccio <casey@deccio.net>
On Tue, Sep 18, 2012 at 1:54 AM, aaron morton <aaron@thelastpickle.com> wrote:
each with several disks having large capacity, totaling 10 - 12 TB.  Is this (another) bad idea?
Yes. Very bad. 
If you had 6TB on average system with spinning disks you would measure duration of repairs and compactions in days. 

If you want to store 12 TB of data you will need more machines. 
 

Would it help if I partitioned the computing resources of my physical machines into VMs?  For example, I put four VMs on each of three virtual machines, each with a dedicated 2TB drive.  I can now have four tokens in the ring and a RF of 3.  And of course, I can arrange them into a way that makes the most sense.  Is this getting any better, or am I missing the point?

Casey



--
Best regards,
 Vitalii Tymchyshyn