Back/restore with dd

[Paul English]

So in the process of trying to recover my files, I made a backup copy of a
partition using dd. I did:

dd if=/dev/ad1s2e of=ad1s2e

So I created a file, the size of the partition sitting on another disk
area.

Now I want to copy that back to another disk partition. I tried just using
dd, but that didn't work:

dd if=ad1s2e of=/dev/ad1s1e

dd if=ad1s2e of=/dev/ad1s1e
dd: /dev/ad1s1e: Read-only file system
2+0 records in
1+0 records out
512 bytes transferred in 0.026033 secs (19667 bytes/sec)

I have created ad1s1e (which is a different physical disk) as a partition
with the same block count as ad1s2e. I used /stand/sysinstall, so it
should have had the same defaults for everything, correct?

What am I missing? Why would it say read-only file system, and then
proceed to transfer only a couple of bytes?

Thanks,

Paul