Raid one

[Karl Larsen]

Les Mikesell wrote:
> Karl Larsen wrote:
>> Les Mikesell wrote:
>>> Karl Larsen wrote:
>>>
>>>>> RAID is generally used because of a need, rather than simply 
>>>>> because you
>>>>> can do it.  Of course, if you're doing this as a learning exercise,
>>>>> that's another matter.
>>>>>
>>>>> Some benefits of RAID, depending on the type, *can* be faster 
>>>>> access to
>>>>> data spread over more than one drive (though your current system 
>>>>> might
>>>>> be more than fast enough, making this pointless), or having a spare
>>>>> drive that *can* let you keep on working when one drive has failed
>>>>> (mirroring - useful for servers, probably less important for stand 
>>>>> alone
>>>>> client machines in the home), or increased storage space by using an
>>>>> array of drives as if they were one big one (which can also be done
>>>>> using LVM).
>>>>>
>>>>>   
>>>>    No my need is to have a backup in case this hard drive quits 
>>>> working. I can do this with rsync. But I am getting the data needed 
>>>> to make a raid-1 and it would be fun to make one just for the 
>>>> experience :-)
>>>
>>> Disk failure is the most likely thing to go wrong, just not the only 
>>> thing so you still need some other kind of backups.  Raid has the 
>>> advantage that you can recover more quickly if you go down at all 
>>> (IDE drive failures often hang the computer until you remove them) 
>>> and you don't lose the data past the last backup run.  Disks are 
>>> pretty cheap these days and they fail unpredictably about like light 
>>> bulbs.  If you want to make things slightly easier, set up a machine 
>>> with 3 or 4 disks and don't bother with raid on the system portion 
>>> which you can easily re-install.  Just add a pair of drives with one 
>>> big parition in a raid1 configuration and move your /home to it - or 
>>> set it up that way during the install.  Then you just have to save 
>>> or remember any special configurations in /etc and keep your 
>>> important work under /home.
>>>
>>    I see the white knuckles part is where your trying to copy, for 
>> example /usr/ from the working f7 to the raid-1 partition for /usr/. 
>> It seems that you can drop clear back to a basic window with 
>> Ctrl-Alt-F1 and use after logging in as root, # cp -at /usr /dev/md6. 
>> This should work fine :-)
>>
>>    Still it is a worry. But I see how to do it. Now to write it down :-D
>
> You left out a couple of steps there.  You have to make a filesystem 
> on /dev/mdxx and mount it in some tmp directory for the copy.  Then 
> you do the copy using the tmp mount point, then add an entry in 
> /etc/fstab to mount where you want after a reboot, rename the old 
> directory and create a new, empty one for the real mount point, and 
> reboot.  And you probably want /home instead of /user.   With this 
> approach you don't destroy your existing copy until you know the new 
> one works.  If it fails for some reason (like forgetting to set the 
> partition types to FD and they aren't detected at bootup), you can 
> always boot the install cd in rescue mode and fix things or put the 
> the old directory back.
>
    Yes you have to make a number of partitions on the new hard drive. 
Then you have to make the same number of /dev/md1, /dev/md2 ... /dev/mdx 
where x= number. You do this with:

# mdadm --create /dev/md1 --level=1 --raid-devices=2 /dev/sdb1 missing

Read man mdadm and you will see it IS the raid tool.


-- 

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