freebsd stable - Oct 2016 - HEADS UP: Do not upgrade EC2 instances from 10.x to 11.x yet

[Apologies if anyone gets this twice; the first copy I sent seems to have
been eaten by a mail server somewhere.]

We've identified a bug in the loader(8) in 11.0-RELEASE (to be precise,
FreeBSD 11 after April 6th) which results in it attempting to read past
the end of the disk if the last partition is not aligned to a 4k boundary.
On most (maybe all) physical hardware this results in significant delays
to the boot while the spurious I/O fails; in Amazon EC2, this results in
the instance hanging permanently.

Most systems do not have such misaligned partitions, but the FreeBSD 10.x
images in EC2 do, and will consequently hang on reboot if you upgrade them
to 11.0 (or to 12-current, for that matter).  I recommend not doing this.
The AMIs which have been built for FreeBSD 11.0 have properly aligned
partitions, and are not affected by this bug, so (once the release is out!)
you'll still be able to get FreeBSD 11.0 by launching new EC2 instances.

I imagine that this will be fixed with an errata notice shortly after the
release, after which point it will be safe to upgrade (since you'll end
up with the fixed loader), but as always that will ultimately be up to the
release engineering team.

Thanks to Peter Ankerst?l, Allan Jude, Warner Losh, and Glen Barber for
their help in tracking down this problem.

-- 
Colin Percival
Security Officer Emeritus, FreeBSD | The power to serve
Founder, Tarsnap | www.tarsnap.com | Online backups for the truly paranoid