It sounds like drive 6 is in a predictive failure state and is bad, it possibly caused the array to be corrupted. You should be able to install the OS on the other 5 drives and be fine. You may want to download our 32 bit diagnostics utility and boot to it to test all of the drives.
ftp.us.dell.com/.../DELL_32-BIT-DIAGNOSTICS_5118-3_R212797.exe
Run this and create bootable media. Boot to the disk and choose the 2nd option for hardware diagnostics and run an express test.