How to mirror the FreeBSD OS on two disks

[miles kuo]

Hi all,

I have two SAS disks for the FreeBSD install. I want to install the freeBSD
on one disk and mirror to another disk. Just like the AIX Mirror.

Any changes will sync between the two disks. And if  one disk crashed or
disconnected, the OS could continue running on another disk.

Does the FreeBSD support the disk mirror? How to implement it?