Firstly, to avoid any confusion with terminology I will try to explain what I mean by the term "Forum" in the context of this suggestion.
The vB site has a number of forums. It has football forums (one for each team), a horse racing forum, a general forum and various other forums for different sports. The idea was to migrate one of these forums over initially (say the horse racing forum) so that if there were any problems it doesn't affect the entire site. It would be easier to manage a relatively small forum in the event of problems.
Suggested Approach (non technical)
To distinguish between Xenforo data and vB data I will prefix all data references by X or vB as appropriate
I am having to guess at how the import actually works, so please bear with me. Hopefully I’m not talking complete rubbish but I think, logically, and in broad terms, it will be something like the following.
Phase 1 (Migrate a single forum or selection of forums)
vB Members. Migrate all Members from vB. On import each Member will be allocated a unique ID which I will call the X Member ID). The X Member Name will be set to the vB Member name.
All Members will remain on the vB site until all Forums have been migrated
vB Member PMs. Migrate all vB PMs. Each PM for the vB member will be imported with the vB member Name attached. Where vB Member Name = X Member Name the X Member ID will be used to create an X Conversation record with a unique X Conversation ID being allocated. Using the same X Conversation ID, further X Conversation records will be created for each additional Participant in the PM, Where the vB Participant Name = an existing X Member Name, the X Member ID will be adopted.
All PMs will remain on the vB site until all Forums have been migrated
vB Threads. Import all threads for the selected forum(s). Each post in the thread (including the opening post) will be imported with the vB Member Name attached. Where vB Member Name = X Member Name the X Member ID will be attached to the post and a unique X Post ID will be allocated. Each X Thread will be allocated a unique X Thread ID and posts will be linked to their respective thread via the X Thread ID). All attachments will be allocated a unique X Attachment ID and linked to the post via the X Post ID.
The imported forum will be removed from the vB site and a redirection to Xenforo placed on the All Forums Index
Subsequent Phases (Migrate a selection of forums or all remaining forums)
vB Members. As for Phase 1 but import only those Members registered since the previous import. If the import program does not allows filters the members to be migrated will have to be filtered out first and the import carried out from the filtered file.
vB Member PMs. As for Phase 1 but import only those PMs timestamped after the previous import
vB Threads. As for Phase 1
I think this will allow for the situation where members can engage in conversations on the vB site and the Xenforo site whether or not they have migrated over.
Any comments welcome.