I would like to copy all the posts, users, and pages from my main site into a sub site. I've tried exporting and importing, but the main site has thousands of entries and hundreds of users, and the import seems to fail at around 250 posts without an error. Any ideas for the migration would be greatly appreciated.
Unfortunately, this fine plugin (Add Clone Sites for WPMU (batch)) doesn't do that...
From its FAQ:
Why can't I clone the main site?
I chose not to because the main site can be slightly different in structure than a new network site.
Albeit a little chaotic and difficult to search, there's very good info about MS in WordPress official forum.
I won't do a deep search for you, but if you do, and find a nice method, please post it here :)
which is for importing an existing standalone blog into a network, but can also be used the other way, or to help you figure out how to dupe blogs manually within a network.
Finally, I know that this other one, premium as well, does it: BackupBuddy.
The actual version is still in Beta stage regarding Multisite, and have some glitches (nothing grave) when exporting.
But apart export/import, it also has a duplicate option, that I just tested.
I did it with the Main Site in a local MS and seems ok.