How to force a NFS Export to read-only for all clients

It really depends on what software you're using for the migration. 

WITH RSYNC

If you're just using rsync, or some other host-based tool, then the best approach would be to take all of your existing lists; R/O, RW, ROOT, and CLIENTS, single instance them, and then put all of those IPs into Read Only clients before you do your final copy (except for any systems being used as migration hosts/proxies).  You would also at the same time empty out all the other client export lists, root, rw, clients, etc..  My company's software DobiMiner does this automatically for you, and creates them on the other side.  It's not an easy manual process, and even more difficult when you consider how you would back them up and roll-back if needed.

WITH SYNCIQ

If as you stated above you're using SyncIQ then honestly the best approach is to either

1. Just delete the exports from the source or

2. do the same (move all clients into RO clients) as listed above.  

Then you would perform the final incremental with SyncIQ followed by a failover (allow writes) on the target.

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A BETTER WAY WITH SYNCIQ

But I personally suggest something else altogether.  Redirect your clients to the NEW cluster first, then do the final incremental.  Why in that order?  Because if you redirect them first, they have access to a read-only set of the data on the other side (assuming the matching exports are already in place).  A SyncIQ protection domain will ensure that no data is modified on the target.  Yes the downside is that they're seeing a version of the data that's a few hours old (depending on your SyncIQ frequency), but you can run the jobs in the background, and when they are done, allow writes to the SyncIQ Targets and you're golden.  Leave it like that for a few days, then hit break, to sever the relationship, assuming the old source cluster is going away.

Hope this helps,

~Chris Klosterman

Principal SE, Datadobi

chris.klosterman@datadobi.com