[NTLUG:Discuss] rebuilding a raid5 with bigger disks

[Kevin Brannen]

al hardigree wrote:

>I have a raid 5 array with 8gb hdds
>I want to replace them one at a time with 40gb hdds and let it rebuild each time
>the question is......
>during rebuild, will the raid make an 8gb partition on the 40gb?
>if so, can I grow the 8gb to the full 40gb without taking the array offline?
>  
>

Depends on your controller (hardware or software).  But generally 
speaking, no it won't do that (or so my reading has indicated).

For example, the software RAID howto says, and I quote:

    If you use N devices where the smallest has size S, the size of the 
entire array will be (N-1)*S.

I'm certainly not a RAID guru, but the few hardware controller manuals 
I've read say the same sort of thing.  You're going to need to save the 
data off somewhere temporarily, build your array, then restore your 
data.  You really should have a spare drive even with RAID 5.  Assuming 
your present array is < 6 disks (for 5*8G), then back up your present 
data to the "spare" as an independent disk, build your new array, then 
restore.  Then you can take your spare out and put it on the shelf to 
wait for a failure, or assign it as a hot spare.

That's with the assumption that you only have 1 controller, else it's 
simple. :-)

HTH,
Kevin