Odyssey, meaning "a long journey" is obviously derived from the name Odysseus (Ulysses in latin). Homer himself associates the name with the verb "odyssomai" meaning "to become angered, hateful". Note that the first "y" in Odysseus (as well as osyssomai) is the letter upsilon (Õ).
Odessa in Greek is "Odessos", the "e" being the letter eta (H). This importasnt difference (Y in Odyssey vs H in Odessa) makes it unlikely that the two are connected. According to one source (G. Babiniotis, Hellenic Lexicon), "Odessa" bears unkown proto-hellenic etymology. I strongly suspect however that Odessa is related to the word "Odos", meaning "journey, voyage". This fits in with the fact that Odessa was an imortant port throughout its history. And paradoxically supports Raven 's definition.