What's difference between 2&>/dev/null and 2>/dev/null?

I found my Linux command doesn't work,Which confused me a lot.Here is it.

Test Case

root@ajinlong:/var# cat test.txt 
dsv vm 1
test
dsv vm 2

# No Output
root@ajinlong:/var# cat test.txt | grep "dsv" 2&>/dev/null

# No Output
root@ajinlong:/var# cat test.txt | grep "dsv" 1>/dev/null 2>&1

root@ajinlong:/var# cat test.txt | grep dsv
dsv vm 1
dsv vm 2

It seem 2&>/dev/null equal to 1>/dev/null 2>&1.I haven't seen the Usage .