I know I am late with this reply, but I wanted to plug 
https://github.com/mblakele/task-rebalancer for this job. The downside is that 
it requires 5.0, or some patches for 4.2. But the 5.0 upgrade is very easy: if 
you are already planning on a move to 4.2, consider going to 5.0 instead. You 
can defer reindexing until you are ready.

Assuming you can use it, the task-rebalancer should be faster than XQSync - as 
long as you allocate enough task server threads. The project also provides an 
example module to 'evacuate' a forest. You could modify it to evacuate your old 
forests, which would populate your new one(s).

Along those lines, I wouldn't let a single forest grow without bounds and 
multiple devices are good for performance. Generally speaking I try to make 
sure the database has:

* 1 forest per 2 CPU cores
* no more than 200-GB each
* no more than 32M documents each
* no more than 2 forests per filesystem
* no more than 1 forest per spindle

Some of these rules depend on the situation, too. With positions enabled, for 
example, I would try for something closer to 8M documents or 100-GB, whichever 
comes first. With RAID-1 or RAID-10 I would count drive-pairs as spindles. With 
RAID-5 or RAID-6 I would count RAID groups as spindles.

-- Mike

On 10 Jul 2012, at 19:15 , Tim Meagher wrote:

> Hi Folks,
> 
> I have over 150 GB of content in one database that is currently spread
> unevenly across 3 forests on 3 separate devices.  I need to migrate this
> content to a new database which uses one device with more than enough space
> for all of the content.  Since there is only one device, I'm wondering if
> there is any advantage or disadvantage to using multiple forests.  I think I
> should be able to simply copy the content by creating 3 forests in the new
> database and copying the forests over, but I'd like to know if this is not
> an optimal solution in which case I will need to be a little more
> resourceful about copying the content over.  Perhaps xqsync?
> 
> Tim Meagher
> 
> P.S. Using MOvign content from ML 4.1 to ML 4.2.  Sorry, not yet at 5!
> 
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