The Dorvan sector was a region of space in the Demilitarized Zone. Just outside it lied Portas V. (DS9: "For the Uniform")

In 2373, two class-5 intelligence drones detected a Maquis freighter heading into the Dorvan sector. (DS9: "For the Uniform")

The Dorvan sector presumably contained Dorvan V, though this was not outright stated. Asuming this is the case, it also contained three other planets with similar enviromental conditions.
According to the Star Trek: Star Charts (p. 47), Dorvan sector was located in the Alpha Quadrant.
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