I have a laptop with only one HDD and is impossible add other HDD. The feature "copies=2" of ZFS is the perfect solution for to add redundancy to my /home in the laptop.
I would like emulate the copies=2 option of ZFS with LVM (or other software if you prefer), for example 2 copies of each block of my /home partition.
In this HDD, I have other systems and I use habitually the laptop for testing a lot of new versions of OS, so I need continue using a standard MBR partition table and the changes must be in the partition level.
I will not use ZFS or btrfs for this. If you have other ideas, all are welcome :) .
Update: Like Gilles said, my idea only give me protection from invalid sectors and similar failures for a very limited time. Not for human errors, software bugs or mechanical/electronic failures of my HDD. This is the idea.