> In the dmesg you posted, wd2 gets errrors too.
> 
> ATA electrical specifications assumes 18 inches cables. With longer cables
> you're out of specs, and all sort of things can happens.

I re-used the standard cables for all hard drivers.(I fixed the case ;))
It looks fine with ATA 100 during boot. I'm tring to rebuild the RAID frame.
I will report the result later...

> Note that another thing to look at is the power supply. With 8 hard drives,
> it's possible that your power supply is too short.

There is a double power supply on the server. I think there is no problem
about this.

Thanks for your reply!