Raid one

[Les Mikesell]

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.

-- 
   Les Mikesell
    lesmikesell at gmail.com