[CentOS] raid 1

[Les Mikesell]

CentOS List wrote:
>> CentOS List wrote:
>>>> CentOS List wrote:
>>>>>>>>> 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.


> 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?

-- 
   Les Mikesell
    lesmikesell at gmail.com