Debian has a [FAQ http://svn.debian.org/wsvn/pkg-mdadm/mdadm/trunk/debian/FAQ?op=file&rev=0&sc=0] on Linux raid. Some comments:
Answer 4b: The FAQ says that for a 4-disk raid10 array, if one disk has failed, you can survive a disk failure in half the cases. The real figure is that in 2/3 of the cases you can survive.
Answer 6: The raid10 layout actually makes sense with only 2 disks, the FAQ says 3 disks are needed.
The FAQ references http://aput.net/~jheiss/raid10/ which actually does not refer to current Linux kernel raid10 technology, but to RAID1+0 versus RAID0+1 nested raid layout.