raid-one

[Karl Larsen]

Les Mikesell wrote:
> Tim wrote:
>> On Thu, 2007-08-16 at 08:11 -0600, Karl Larsen wrote:
>>>     Hi Tim, I think you suffer from a fear of "fisk" :-)      Yes you
>>> do need to be careful. Look at it this way:
>>
>> No, I don't.  Whatever "fisk" means...  ;-)
>>
>>>     If your going to make a software raid-1 on Linux you must use a
>>> root Terminal. A root Terminal is capable of deleting your entire
>>> Linux! :-(
>>>
>>>     This paper is not for a person who has no knowledge of root and
>>> what it can do. You need to know the basics. I will add a place where
>>> they must show this basic knowledge or not try to do raid-1.
>>
>> Now you're going off on a tangent.  The only disclaimer needed, as
>> already mentioned by us, is to point out changing drive structures is
>> potentially destructive.  Make backups before altering a pre-existing
>> system.
>
> With his approach he doesn't change the existing drive until the new 
> one is known to work.  The potential failure mode is that you get the 
> wrong device name for the fdisk or mke2fs steps.  There's not much 
> sense in trying to describe Linux device names for anything but hd? 
> devices since they are essentially randomized, so the user will be on 
> his own there regardless of what you write anyway.
>
>> What I see you doing, and everything you've said leads to this
>> conclusion:  You're making the classic mistake of over-simplifying
>> something to the point that you completely ignore necessary aspects.
>
> It really will boil down to a very simple set of steps:
>  fdisk the new target partition
>  mdadm create a raid device with a missing mirror
>  mkfs a filesystem on the md device
>  mkdir a temporary mount point
>  mount the md device on the tmp mount point
>  copy the files from the old filesystem to the new.
> repeat for all filesystems
>  either label the new filesystem to match the old or fix fstab/grub.conf
>  install grub on the new disk
>  swap disks
>  reboot
>
> Once it all works with the new disk, fdisk the old one to match if it 
> didn't already and mdamd --add the mirror partitions.
>
> The tricky parts are dealing with what happens if you make duplicate 
> filesystem labels and making the new drive bootable.  But those can be 
> fixed with a rescue-mode boot.
>
Well guys I just set up my first raid-1 system. Here is what it said:

[root at k5di etc]# cat /proc/mdstat
Personalities : [raid1]
md5 : active raid1 sda5[0]
      5124608 blocks [2/1] [U_]
     
unused devices: <none>
[root at k5di etc]#

I did this over lunch and it took several fdisk efforts lots of root 
terminal things like mkfs and cp -a and such but now on this computer is 
all of f7 /dev/sdb5 and on the other hard drive I have /home at 
/dev/sda5 through the raid 1 system. It appears to be working fine and 
to do the whole thing requires more repeated things and another step to 
get grub happy :-)



-- 

	Karl F. Larsen, AKA K5DI
	Linux User
	#450462   http://counter.li.org.