Chris,
Which C* version are you running? 
You might want to do an upgrade to the latest version before reducing the vnode counts, a lot of fixes and improvement went in lately, it might help you getting your repair faster.

H

On 5 Aug 2013, at 12:30, Christopher Wirt <chris.wirt@struq.com> wrote:

Hi,
 
Im thinking about reducing the number of vnodes per server.
 
We have 3 DC setup one with 9 nodes, two with 3 nodes each.
 
Each node has 256 vnodes. Weve found that repair operations are beginning to take too long.
 
Is reducing the number of vnodes to 64/32 likely to help our situation?
What options do I have for achieving this in a live cluster?
 
 
Thanks,
 
Chris