[CentOS] raid 1

[CentOS List]

>>>>>>>>>> I am running raid 1 on a centos 4.4. One of the harddisk (sda1) 
>>>>>>>>>> failed. How can i carry on running the server using only sda2?
>>>>>>>>>
>>>>>>>>> Generate a grub floppy and use that to load the grub menu from 
>>>>>>>>> the sdb (probably now sda) disk.
>>>>>>>>>
>>>>>>>>> If you are really talking about sda1 and sda2, those are 
>>>>>>>>> partitions on the same disk.
>>>>>>>>
>>>>>>>> Is there a detail step by step howto? The raid 1 has no LVM. just 
>>>>>>>> md0, md1 and md2. md0 is /boot, md1 is swap and md2 is the 
>>>>>>>> storage. I had replace sba with a new disk. I tried to boot up 
>>>>>>>> and it says kernel panic. How am i going to reconstruct the raid 
>>>>>>>> and sync sdb to sda?
>>>>>>>
>>>>>>> It might be easier to swap the old sdb into the sda position so 
>>>>>>> you'll boot from it, but you should also be able to boot the 
>>>>>>> install cd with
>>>>>>
>>>>>> If swapped and booted, and got a kernel panic error.
>>>>>
>>>>>>> 'linux rescue' at the boot prompt, let it detect and mount your 
>>>>>>> system (which will be the 'broken' raid devices with their single 
>>>>>>> members),
>>>>>>
>>>>>> If i use linux rescue, The 3 mds I created are gone. /cat 
>>>>>> /proc/mdstat says Personalitlies: [raid0] [raid1] [raid5] [raid6], 
>>>>>> no longer Personalities : [raid1]
>>>>>
>>>>> Perhaps your raid wasn't really working the way you thought before. 
>>>>> From the rescue boot, does fdisk show the 3 partitions on the old 
>>>>> disk with type 'fd'?  Can you mount the old /boot and / partitions 
>>>>> somewhere by hand?  You should be able to do this with the /dev/sda1 
>>>>> and /dev/sda3 device names if the md devices aren't detected at boot.
>>>>
>>>> cat /proc/partitions still shows me the 3 partitions.
>>>
>>> Does fdisk say that they are type 'fd'(raid autodetect)?
>>>
>>>> I actually copied /boot to the "replaced disk" and it is able to boot 
>>>> up, but without any filesystem, so i guess the boot is still intact. 
>>>> So do i need to mount /boot and /?
>>>
>>> If you can get the original partitions to be detected as their md 
>>> devices you should fdisk matching partitions on the replacement disk, 
>>> then 'mdadm --add ...' to add them and they will automatically sync up.
>> 
>> mdadm --create --verbose /dev/md0 --level=1 --raid-devices=2 /dev/sda1 
>> /dev/sdb1
>> mdadm --create --verbose /dev/md1 --level=1 --raid-devices=2 /dev/sda2 
>> /dev/sdb2
>> mdadm --create --verbose /dev/md2 --level=1 --raid-devices=2 /dev/sda3 
>> /dev/sdb3
> 
> If you already had raid devices on one of the disks you should not have 
> had to --create them again.  The original ones should have been detected 
> and you should have been able to --add new matching partitions.

I created them as md(s) are not longer there.

> 
>> After that i reboot and got the kernel panic again.
>> 
>> md: considering sdb1
>> md: adding sdb1
>> md: created md0
>> md: bind<sda1>
>> md: running: <sdb1><sda1>
>> raid1: raid set md0 active with 2 out of 2 mirrors
>> md: ... autorun DONE
>> md: autodetcting RAID arrays
>> md:mautorun ...
>> Creating root device
>> Mounting root filesystem
>> switching to new root
>> switchroot: mount failed: 22
>> umount /unitrd/dev failed: 2
>> Kernel panic
> 
> When you --create a new raid it will start to sync the mirrors.  It may 
> have done this the wrong direction, overwriting your old contents.  Can 
> you still do a rescue mode boot, mount /dev/sda3 (or sdb3 if the old 
> drive is in the 2nd position) and see the contents?

I am unable to mount sda3. 

# mount /dev/sda3 /mnt/part3
mount: Mounting /dev/sda3 on /mnt failed: Invalid argument 

sdb is not longer detectable.