USB Drive Software Disk Mirroring - Is this the right approach?

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http://unix.stackexchange.com – I have a 1TB NTFS USB Data Drive (no boot, etc...) that I would like to keep a mirror of as a backup in case of hardware failure. It is always connected to my raspberry pi running the raspbian (debian) based raspmc. After reviewing this question... How to set up disk mirroring in Ubuntu? This seems like a good solution to mirror the drive. Will this work as expected for USB drives? Am I looking at any performance loss by mirroring the drive? Anything I'm not considering that I should be? (HowTos)