I need to set up a RAID 1 array on Squeeze. I have 3 partitions: sda1 is root, sda5 is home, and sda6 is swap. (sda2 is the extended partition containing home and swap. This was a clean installation, so I don't know what happened to sda3 and sda4...)

All the information that I've been able to find recommends doing something like this:

mdadm --create --verbose /dev/md0 --level=mirror --raid-devices=2 /dev/sdb1 /dev/sdc1

Do I need to type a separate command for each partition, or is there a better way to do it? Also, should I use the UUID instead of the dev names?

Yes, you do have to do that separately for each partition. You don't have to do that for the swap partitions, if you mention them both in your fstab the kernel will automatically choose a scheme to use them.

Regarding sda3 and sda4, they are reserved for primary partitions, logical partitions in an extended partition will start at sda5, so this is normal behavior, don't bother with that.

The easiest way to set up a RAID 1 is to install to a single disk, then add the 2nd to the array and have the kernel do the copying

When I upgraded my RAID 5 setup in my fileserver (from 3x 500G to 3x 2TB) I exchanged one 500G disk with a 2 TB one, then have the kernel recreate the filesystem on that disk for 24 hrs, repeated twice more, then simply enlarged the filesystem (XFS) on the RAID. So, instead of 1TB I now have 4 TB in RAID to full up (up up up up up up up sorry, there's an echo somewhere down there there there there there there )

Thanks for the answers. So should I mirror sda1 to sdb1 and sda5 to sdb5? In other words, hook up a blank drive on the next SATA port and run:

mdadm --create --verbose /dev/md0 --level=mirror --raid-devices=2 /dev/sda1 /dev/sdb1
mdadm --create --verbose /dev/md0 --level=mirror --raid-devices=2 /dev/sda5 /dev/sdb5

That is the way I do it for my /home partition, except that I use a RAID 0 for it.