[CentOS] Mirroring disk.

OK all my HP Microserver is purring away nicely now, as usual I
looking for the rainy day.

Although my data is on a RAID 5 array my OS is on a single disk.

Any suggestions as to the best way to have a copy of my OS on an
attached USB Drive?

Been considering dump and restoring to the usb disk periodically? or
maybe something using LVM or maybe creating and breaking a RAID 1
array?

Just not sure of the best plan at the mo.

Any tips?