A friend who upgraded a system from 10.3, which previously ran various 10.x releases, and was originally installed probably as a 9.0 system. Always upgraded via freebsd-release. Anyhow - successfully upgrade to 11.0 Release, and commented that two items that were not documented in the release notes that probably should be noted for people planning to upgrade. Both issues are ZFS related: 1) The new support for sha512 and skein checksums in a zpool was not documented. This is important in that 'zpool status' (after upgrading) will complain that the zpool version is out of date until 'zpool upgrade -a' is run. A possible improvement to the code (outside the scope of this issue), would be to have a mechanism to have the acknowledge of the feature, but warning suppression. If the user DOES do a 'zpool upgrade -a', they then need to install fresh bootblocks. Which leads to item #2... 2) The increased size of the /boot/gptzfsloader in 11.0 vs prior releases. The machine in question was installed probably with 9.0, when the 'best practices' was to have a 64k boot partition. Well, the gptzfsloader code is now ~88K, and does not fit in the existing partition. A warning about potentially needing a bigger freebsd-boot partition is required for people upgrading older releases, least they upgrade their zpool and then be stuck without the ability to upgrade their bootblocks. (As it turns out the user was able to reclaim a 'gap' in the partitioning and get the bootblocks upgraded without having to reload the system from scratch.)
*** This bug has been marked as a duplicate of bug 213676 ***