My main computer HD is also in raid 1 so I'm not worried about mechanical failure. My only risk is unwanted deletion.
I don't have any raid
I just have one 500Gig as system and one 1Tera as Data...
...in my primary system
My backup system is a computer built identically as the first apart from the speed of the CPU and the graphics card...
... again with 500Gig plus 1Tera
I make a backup to the secondary system before I delete my 16GB flash card in the camera, so at any given point in time I always have at least two copies of every picture apart from those images I just shot before I returned home. These backups occur once a week or once a month the latest.
1. you never lose something due to HD-crash
2. you never lose something due to a delete/format/defrag action
3. you never lose something due to a virus break out on one computer
As to the disks: I use maxtor and Hitachi. Just gave 2x Samsungs new 1Tera back due to unprecedented problems.
Mobo: I went for Gigybyte after a series of probs with Asus
CPU: Intel Core 2 Duo 6600 at 3GHz + 2 GB RAM, WinXP Prof
Printing: CanonPixmaPro9000 / Viewing: NEC 2690 WUXI
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