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Offline defrag of Exchange 2010 DAG DB

Please do not just tell me I don't ever need to defrag, thanks.

I am having a problem with my email archiving solution at the moment which should be resolved shortly. This has lead to my two DAG'd DBs getting dangerously close to filling their partitions.

I have installed a new partition on all the DAG servers and I will be creating a third DB soon to spread the mailboxes out.

Once the archiving solution comes back and mailboxes are shrunk I want to know how much free space there actually is on my two original partitions.  So while I have this empty third partition before I create the third DB, I have the chance to either (A) create the third DB and shuffle all mailboxes to it from each database one at a time recreating the other two databases in the process or (B) use the space to offline defrag the other two DBs.

The reason I don't want to do (A) is that one of the nodes of the DAG is in another office and it would take a looooong time for it to catch up with all the moving around of mailboxes.

So I would prefer to do the defrags, however I can't find the procedure to do this with regards to DBs in a DAG. Every post on t'interweb is just answered with you don't need to do it.

I know the DB files won't grow while there is space 'in side' them but I want to know exactly how much free space I have so that I can effectively balance the final 3 DBs.

I could in theory bring the third EX server back to this office for the dance of the mailboxes but that would be a pain and only worth it is the defrag process is extremely painful or dangerous.

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Ok thanks, would you say this is the sensible option over moving the third EX box back to head office and then moving/recreating DBs?
if you wanted that third to be a DR server, no
you just need to make sure that in the main site you have a majority so that if you lose the WAN your main site will stay online
the remote site would lose majority and go offline
sorry, misunderstood the question

yes, depending on the size you don't want to generate a lot of wan traffic
i also should have added once the defrags were complete on all you would resume the database copy, but you probably already knew that
Yup, is reseeding after defrag likely to create long update queues anyway or should the copies all still be up to date?
the database will still be up-to-date
you are suspending the database copy which will stop log replication
to defrag the database you must dismount it which prevents any new logs

Great that is what I wanted to hear. Reading around it seems like 110GB DB could take a looong time to defrag, any guesses?
if you defrag it to the same disk where the db lives, it will probably take about 4-6 hours
it also depends on the i/o of your disk
i had an 80gb db take 3 hours, but there was a lot of white space

check the application log for 1221 events to see how much
I can defrag to separate disks so it should be quicker I guess.
it's quicker on the same disk
separate disks it must copy the new file to the original location
same disk doesn't copy
oh that's bad news I've not got enough room on the same disk.
yes, think about how long it takes to copy a 110gb file from disk to disk :(
Thanks for the help :)