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I bought the 1.5TB version of this one for my new iMachttp://eshop.macsales.com/shop/firewire/1394/USB/EliteAL/eSATA_FW800_FW400_USB

My iMac hard drive is 1TB and is about 50% filled with photo files. I partitioned the external so one partition clones the iMac and another partition is used for Time Machine. I use Carbon Copy Cloner, included in the purchase plus a $10 donation, and it works greats. I backup about once/day for each type.

Then once/week I clone make another clone backup using the Voyager Q and my spare hard drives. This device is great in that you can use and store offsite any number of drives or different sizes for backup. I use this with several drives for my iMac and also to backup my MB
http://eshop.macsales.com/shop/NewerTech/Voyager/Hard_Drive_Dock

These two along with Time machine and Carbon copy (or Super Duper) gives me plenty of flexibility and lets me use all my extra drives as needed. Also, since they are not dual setups, there is no fan and thus very little background noise
 
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