It will make your life *a lot*  easier by doing a 1 to 1 migration from the 0.6 cluster to the 1.X one. If you want to add nodes do it once you have 1.X happy and stable, if you need to reduce nodes threaten to hold your breath until you pass out.  

You can then simply:
* drain and shapshot the 0.6 cluster. 
* rsync data to the  1.X cluster and copy the configs (with necessary IP changes etc). 
* turn on the 1.X cluster
* scrub

Your roll back is to switch back the 0.6 at any time. 

Last time I did a 0.6 upgrade I did partial migrations to the live system so I could then do a final delta migration when the site was down. This was done to reduce the down time when we turned the 0.6 off. It also meant we could test the app against the 1.X cluster with stale production data *before* the big switch over. 

As always read the NEWS.txt for instructions, you will want to go all the way back to the 0.7 instructions. 

Cheers
 
-----------------
Aaron Morton
Freelance Developer
@aaronmorton

On 3/02/2012, at 7:24 AM, Josh Behrends wrote:

I'm new to administering Cassandra so please be kind!

I've been tasked with upgrading a .6 cluster to 1.0.7.  In doing this I need a rollback plan in case things go sideways since my window for the upgrade is fairly small.  So we've decided to stand up a brand new cluster running 1.0.7 and then stop the old cluster, snapshot the data, and then move it over to the new cluster.  

So I need to know, can I use sstableloader to take the snapshot data from my .6 cluster and stream it into my new 1.0.7 cluster?  I should also note that the new cluster MAY NOT have the same number of nodes either.

Josh