2nd drive failure in a raid 1 need advice

[SweepingOar]

My 2007.0 install had some major problems after about a year of trouble free service so I decided to try 2008.0 beta amd64. It installed fine, usual newbie hiccups, and I noticed a lot of seekcomplete (or something like that) errors while installing files and unpacking tarballs. Finally the drive that gave the errors stopped working entirely (it's a Western Digital sata drive) and cat /proc/mdstat gave me [_U] for boot and root partitions. Swap was also raid1, but for whatever reason it wasn't reporting any problem. I took the failing drive out (had to use the smartutils or whatever to figure out which drive was the bad one) and got a warranty replacement drive from WD (that looks a little more used than mine). I copied the partition table and added the new drive to the array and it rebuilt fine and the machine ran fine for a day or three. Today I rebooted the machine and it would not get to grub. I swapped the new drive's sata data plug on the motherboard but that didn't help. Then I just unplugged the "new" drive and the machine started up fine (raid only using the one drive now though). Grub is installed on both sata drive's mbr. The drive that failed originally and now failed again was sda. I'm thinking that the problem was that sda failed and the motherboard looks to that drives mbr and then hangs if there is a certain type of issue.

My question is where to go from here. I put the failed drive into my mac and I'm zero-ing all the data and I'm going to try to install it into the raid again. Should I request a different replacement drive from Western Digital? Should I replace the sata cable? Try a different motherboard? What would be the next logical step? Thanks.
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-SweepingOar

[alex.blackbit]

i would attatch the drive with the same cable to the same machine, but not in a raid set.
format it, and stress it somehow to see if it produces errors. then boot from that single drive.
that will tell you if the combination of drive, cable and motherboard like each other.
if everything is fine, try to re-attach it to the raid set.

[SweepingOar]

Damn! I just realized what I probably did wrong. Grub was on both mbr's before the first drive failed, but when I put the new drive into the array I think i forgot to put it on there. The question is, if there are two good drives in a machine, why would it only look to sda to boot?
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-SweepingOar

[alex.blackbit]

maybe you told your bios or efi to do so.