How to Upgrade Drives in a DMRAID config?

[Laszlo <laszloacs@gmail.com>]

I have a Ubuntu 11.10 system upgraded to latest everything and have a
/Data partitioned on 4 - 320Gb drives configured using DMRAID as a RAID5
array.  I recently acquired a bunch of 1.5Tb drives and figured I'd
upgrade my array with 4 bigger drives, one at a time.  My thought is
to fail one drive at a time, replace that drive with a new 1.5Tb drive
and rebuild the array until all 4 drives have been replaced.  Then,
I expect to expand the array to utilize the additional space made
available.

The problem is I can't seem to determine how to fail a drive.  I
tried simply removing one, but that doesn't appear to put the array in a
state where I can simply add a drive in the missing slot.  Google is
no help so far. 

My system has an NVIDIA chipset with RAID disabled on the Mobo BIOS and
this array was not configured using any MOBO or BIOS tools.  I
remember that I had to use DMRAID a couple of years ago instead of MDADM
since the NVIDIA chipset had a problem with MDADM.  Here's a little
more info from the machine:




~$ cat /proc/mdstat
Personalities :
unused devices: <none>

~$ sudo dmsetup info
Name:              
nvidia_aafjfffa1
State:             
ACTIVE
Read Ahead:         256
Tables present:     LIVE
Open count:         1
Event number:       0
Major, minor:       253, 1
Number of targets:  1
UUID:   DMRAID-nvidia_aafjfffa1

Name:              
nvidia_aafjfffa
State:             
ACTIVE
Read Ahead:         3072
Tables present:     LIVE
Open count:         1
Event number:       167007
Major, minor:       253, 0
Number of targets:  1
UUID:   DMRAID-nvidia_aafjfffa

~$ sudo dmraid -r

|----------+--------+------------------+----------+---------+----------------+---------| 
| Device   | Format |
Name            
|   Type   | Status? | Size (sectors) |
?       |
|----------+--------+------------------+----------+---------+----------------+---------| 
| /dev/sde | nvidia | nvidia_aafjfffa  | raid5_ls |
ok      |     
625142446 | data@ 0 | 
| /dev/sdd | nvidia | nvidia_aafjfffa  | raid5_ls |
ok      |     
625142446 | data@ 0 | 
| /dev/sdc | nvidia | nvidia_aafjfffa  | raid5_ls |
ok      |     
625142446 | data@ 0 | 
| /dev/sdb | nvidia | nvidia_aafjfffa  | raid5_ls |
ok      |     
625142446 | data@ 0 | 
|----------+--------+------------------+----------+---------+----------------+---------|




I don't want to trash my existing array and lose any of it's
content.  Creating an additional array in this box is not an option
since I've already used up all the available connections and have no
internal physical space to add 4 drives.  Anyone have any idea how
to proceed with my project?

-- Laszlo