[arch-general] Software RAID w/ 4 Drives Fails

[Carlos Williams]

On Fri, Jan 22, 2010 at 2:34 PM, Robert Howard <rjh0507 at ecu.edu> wrote:
> RAID5 is one of the levels that can be added to after creation. I think you
> should boot from the install CD and read the mdadm man page. It contains all
> the information you need to do what you want. That said, when you try to
> build the 4-drive array, do you get any errors reported? You may need to set
> the partition type to Linux MD RAID for the new drive if you intend to use
> the mdadm hook to assemble the array.
>
> On Jan 22, 2010 1:15 PM, "Dwight Schauer" <dschauer at gmail.com> wrote:
>
> Can you add a drive to an array after it has been built?
>
> I know you can add a hot spare, or remove a drive and add another, but I did
> not think you could increase N, where the size of the array is N-1 * size of
> each drive. How is the raid going to know which is data and which is parity?
>
> Of course I could be wrong.

I don't doubt that I could build a working Arch system with 3 physical
drives and then use 'mdadm' to add the 4th drive as a spare or as
additional disk space for the RAID5 array. I should be able to add a
4th disk to RAID5 w/o having any 'hot spares, correct?

I just feel that I should be able to do this from a fresh install. I
assumed I was missing a syntax in the command. I partition all 4 disks
identical. All disks have a equal amount of partition space assigned
to RAID (type = fd) and then I use mdadm to build the array so I can't
see why it does not work. Yes I do have a USB keyboard but if I don't
need to add the usb modules for RAID5 with 3 disks, why would I need
to add it for RAID5 with 4 disks. It makes no sense to me...