Upgrading from Version 10 to version 11 - Synchronization configs lost

We did go straight from 10.2.1 to 11.4.x. The biggest catch that we ran into was iRule and bigip.conf syntax changes, and as Hannes pointed out, to effectivly edit them you need to understand the differences in syntax. It can be done, but may be worth your while to go in stages. Did you get any kind of error? I do recall one pair that we did, for some reason would not upgrade with port-mirroring setup, but none of the other pairs we did gave us that issue.