RAID 1 isn't going to give you better performance ... it is intended to protect your data from exactly what you experienced with the single failed drive (so it did its job). The issue is not Windows 7 on a RAID 1 ... it is most likely a driver issue:[URL] You might try loading the drivers for Vista x86 (supported on the E510 - Windows 7 is not officially supported, so Dell has no drivers for Windows 7, but we can get one from somewhere else if this one doesn't work):[URL]  
My Dimension E510 was purchased with a 2-disk Raid1 configuration, XP Media Edition. Wanting to extend the use of this system (with the April 2014 support deadline approaching) I purchased a copy of Windows 7 Professional, and two 1TB Western Digital drives. 1. After installing the 2 "blank" drives, I started the system and hit Ctrl-I to setup the Raid1 array. 2. I inserted my Win7 installation disk, rebooted, and began the installation.  (The installation recognized a "single" drive, which I believe is reasonable since I had configured the Raid1 array). 3. The installation seemed to proceed normally.  Went through the "coping files...", etc., and restarted. 4, After the restart, the installation continued for a while, in the "completing the installation" part.  (The progress bar at the bottom of the screen was nearing the end.) 5. Then, a message box was displayed, saying that 'Windows could not be installed on this hardware configuration'. Is there some way to complete this installation successfully??  The system ran well under Windows XP.  (I had rebuilt a single failed drive once, but never needed to reinstall the OS). It if is, in fact, not possible to install Win7 with Raid1 on this machine, I'll break the array and complete the installation. Just thought that I could get a little faster performance with the Raid1 array. Any help on this would be appreciated!
Clean install of Windows 7 on Raid1 failure