Hey,

1. One of my hdds failed (sda) in software raid 1. I rma'd the hdd to western digital and got another one. Now do I have to format it before putting it in my centos server? If yes, how do I format?

2. Also since sda drive failed, i gotta mark sda as failed in raid. Then remove the sda hdd, and pop in the new hdd for sda? Or do I switch sdb to sda and put the new hdd in sdb's place?

3. After that add it to raid correct, then once raid rebuilds I have to do grub? Can grub be done via ssh only? or do i need to be at the datacenter or get kvm?

4. Last question, i've got a supermicro hotswap hdd case, so do I need to shutdown server while I replace the hdd's? Thanks for any help guys, I just want to be sure I do this correctly.

The following is the guide that I will be using, please look at it and let me know if that is the correct procedure:
http://howtoforge.org/how-to-set-up-software-raid1-on-a-running-system-incl-grub-configuration-centos-5.3-p4

Another thing, when the hdd (sda) failed i put it back into raid, but the hdd has bad sectors that is why m replacing it.

1 & 2. http://www.howtoforge.com/replacing_hard_disks_in_a_raid1_array

3. http://wiki.centos.org/HowTos/SoftwareRAIDonCentOS5 - see Section 2 for GRUB info. Whether or not you need to be there depends on 4. and whether or not the system is currently bootable.

4. Thought that's what hotswap is about, but truthfully I haven't a clue.

Thanks for the reply. So that guide is pretty much the same as the one I posted. It's just that someone told me if sda fails then the procedure becomes a tiny bit different. If someone has experience with this do let me know. But I think I have to shutdown the server even though it's hotswap. Then, move sdb to the place of sda and put the new hdd in the place of sdb.

So with method 2 the grub can be installed from home via ssh. That's great, does it matter if one of the hdd already has grub installed on it? If I redo grub on it will it cause any issues?

If GRUB is already working on one member of the RAID there's no reason to redo it on that disk. It should not hurt, but if it ain't broke, don't fix it.

Okay, I will be at the datacenter on Monday and see how things go. If I have additional questions, I will come here. Thanks.

So I was at the datacenter and I replaced failed hdd which was sda. Switched sdb to sda's place and popped in the new hdd in sdb's place. Added it to raid and it started the rebuild process. Now I haven't done grub. Since I moved the hdd sdb to the place of sda and it became sda. I am unsure which hdd is hdo and which is hd1...

Is there a way to see grub current setup? Or should I just the run following commands via ssh (grub):
grub> device (hd0) /dev/sda
grub> device (hd1) /dev/sdb
grub> root (hd0,0)
grub> setup (hd0)
grub> root (hd1,0)
grub> setup (hd1)
grub> quit

Should I just run the above commands and hope it doesn't mess anything up?

(hd0) is /dev/sda unless the mapping has been changed. Should not hurt to install GRUB on both devices.

So then sda has already grub. To install grub on sdb only do I run the following commands:

grub> device (hd1) /dev/sdb
grub> root (hd1,0)
grub> setup (hd1)
grub> quit

Thanks for replying to my questions you are the only one

Glad to be of assistance.