Edit Sat Oct 27 17:03:42 CDT 2012:
While it's true that you can work with the RAID 10 array before it's finished re syncing, I figured that I would answer the question about how to pause during the re-sync process anyway.
This is how you pause the script for the re-syncing process (IMO/AFAIK/etc.):
# Add this where you want to pause...
while [ -n "$(mdadm --detail /dev/md0 | grep -ioE 'State :.*resyncing')" ]; do
sleep 1
done
To use the example above, the whole script would be:
mdadm --create -l10 -n4 /dev/md0 /dev/xvdh*
while [ -n "$(mdadm --detail /dev/md0 | grep -ioE 'State :.*resyncing')" ]; do
sleep 1
done
mke2fs -t ext4 -F /dev/md0
Please note that the above script is not tested and may contain bugs.