This might come a little late..
dd is the best tool to clone raw disks ( or partitions ), and that's exactly what it does.
it copies raw data regardless ( and unaware ) of what filesystem / structure is on the source ( data + metadata )> so ponder on this for a while, as this actually means it will reconstruct the target exactly the same as the source.
Or shorter > dd'ing a raid member will create a raid member .... which in your case will create a second degraded array....
And that's definitely not what you intended to do...
also while it's true that a raid1 mirrors data, it doesn't mean the raw data of the raid members is identical ( some metadata will differ )
proper procedure for reusing a former raid member is to blank it by using
dd if=/dev/zero of=/dev/sdb bs=4k ( don't copy pasta this > change output device to your needs. )
this will properly zero any data / metadata > this is also a good idea on new disks...
if the raid was used as a system disk > run a live cd ( don't copy from a running system )
repartition / format / mount the cleaned disk
mount the degraded raid array
and copy the raids contents with
sudo rsync -HAXavx /media/raid1/ /media/newdisk/
following is only when raid was a system disk :
alter the UUID's in fstab on the target volume ( find out what the new disk UUID is by running blkid )
copy the boot sector by running dd if=/dev/sda of=/dev/sdb bs=446 count=1 ( and NOT bs=512 like most folks think > using 512 will overwrite your partition table !! )
I'm now assuming the target disk is mounted as /media/newdisk
sudo mount --bind /dev /media/newdisk/dev
sudo mount --bind /sys /media/newdisk/sys
sudo mount --bind /proc /media/newdisk/proc
sudo chroot /media/newdisk/
( and after you altered the UUID's in fstab )
grub-install /dev/sdb ( to make sure you've rewritten a fresh bootloader )
exit ( this returns to your non chrooted environment )