linux - Accidentally overwrote wrong disk with dd, how to recover?

I wanted to dd an image from sdb to sdc, but because one hour before I had set up things differently, I just copied the same command:

dd if=/home/user/Downloads/ubuntu.iso  of=/dev/rsdb bs=2M; sync

sda = internal hard drive
sdb = USB hard drive (booted from right now)
sdc = USB stick

There are 3 partitions on the hard drive I've booted from, I guess the other 2 are in read only mode, and the error in shell as I tried two times:

568328192 bytes (568 MB) copied, 38,5818 s, 14,7 MB/s
dd: error writing ‘/dev/rsdb’: No space left on device
715128832 bytes (715 MB) copied, 17,1752 s, 41,6 MB/s

Now I realized I overwrote 1GB over the hard drive I'm booted from (using rsdb). I haven't turned off my computer. Will I loose all data on this drive? Can I recover anything now?

Here’s my /proc/partitions:

   8        0  156290904 sda
   8        1  154218496 sda1
   8        2          1 sda2
   8        5    2069504 sda5
   8       16  244198582 sdb
   8       17   31457280 sdb1
   8       18   20971520 sdb2
   8       19  191768576 sdb3
   8       32    2011136 sdc
   8       33    2011135 sdc1