challenging RAID reconfiguration
 

I would like to perform a RAID reconfiguration of my home server running Debian 5.0.. But after a lot of thinking this proves to be quite challenging...

My current situation is as such:
I have 3 disks of 250Gb in a software RAID 5 configuration containg data
and one stand-alone 85Gb disk containing the operating system itself.
But I would like to have:
4 disks of 250Gb with one partition in RAID1 (/boot) two partitions in RAID5 (one for the rest of the OS and one for the data)
And remove the 85Gb disk from the system

All I have is one disk of 250Gb (which I want to add to the server) and one (hot-swap) free sata port which I normaly use for performing backups to external disks, but which I now can use for the migration process.

My current RAID 5 configuration is as such:

# cat /proc/mdstat
Personalities : [raid6] [raid5] [raid4]
md0 : active raid5 sdb[0] sdd[2] sdc[1]
488396928 blocks level 5, 64k chunk, algorithm 2 [3/3] [UUU]

unused devices: <none>

and as you can see here, I have used whole disks as PV instead of partions on disks.

I was thinking about creating a partition of the 200Gb on the extra 250Gb disk and trying to add this partition to the current RAID 5. But I'm afraid that won't be possible without first shrinking the current RAID5 to 200Gb/disk.. But how can I do that?..

A possible method I was thinking about is removing a disk from the current RAID5, leaving it degraded. Then constructing a new 200Gb partition/disk RAID 5 on the extra disk and the removed disk from the other array.. and copy all the data from the old RAID5 to the new one. Then removing the old RAID5 and adding those disk to the new RAID5, growing the array.
After that I can create aditional partitions for /boot RAID1 and OS RAID5 as I would have 50Gb free on every disk.

But here I think I again bump into a problem: a RAID 5 needs at least 3 disks, so I won't be able to create that new RAID5.. Or is it possible to create an initialy degraded RAID5 with 2 disks and copy all the data over from a degraded RAID5 to another degraded RAID5?

Or does anyone see another solution to this problem?