I have two identical 1TB Western Digital Elements external hard drives. I currently use one for Time Machine and the other is just sitting around. I would like to have a backup for my Time Machine drive in case it fails. To create this backup, I am considering using Disk Utility to create a Raid 1 (mirror) using the two identical drives. After making the raid, my Macbook should see the drives as one unit and I should be able to use the raid as my Time Machine. Thus, any time Time Machine performs any function, it should perform the function for both drives. If one fails, I should be able to replace one drive and allow it to rebuild. Does anyone use this system? Does this sound like a good system? Given that I have a second identical drive just sitting around, are there really any drawbacks to this system? I should note that I also have an offsite Time Machine backup, but it's one that I can only update about once per month. Thanks for your guidance.