FreeBSD System Disk Mirroring with GEOM Step-by-Step

I was asked by co-workers how to establish a RAID-1 (mirror) for the system disk partitions of a FreeBSD 5 system.Giving an answer wasn’t easy for me because in FreeBSD 5 we have multiple possible solutions, each with its pros and cons, and for neither one it is obvious how to deploy it step-by-step without destroying the existing system. Especially if the constraint is to migrate the production system fully remotely from the plain single-disk to the mirrored two-disk setup. I have chosen the newer GEOM mirror class because IMHO it currently is both the most flexible and robust solution and especially works for the boot partition without tricks, too. Nevertheless the necessary steps are not obvious for a FreeBSD administrator, so I’ve written them down in detail as one of the possible answers to this FAQ about mirroring system disk partitions.


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