When I record students in order to analyse their pronunciation, I always ask the question 'What did you do in your last vacation'.
Occasionally, some of them look perplexed. And I have realised it is because they hear the last word as vocation rather than vacation.
These two words would probably not be confused by most speakers in Brunei or Singapore, because they would have [eɪ] in the first syllable of vacation and [oʊ] in the first syllable of vocation. In contrast, the two words are homophones for me, as I have [ə] in the first syllable of both words.
This reminds me that my style of speech is not necessarily the clearest way of speaking. And I should remember to avoid vowel reduction in some circumstances. In fact, having [eɪ] in the first syllable of vacation is probably the most common way of pronouncing the word around the world, and I should remember to adopt this pronunciation.
I just checked in The Longman Pronuncation Dictionary (J. C. Wells, 2008, p. 868). It seems that use of [eɪ] in the first syllable of vacation is preferred by 61% of people in Britain, and it is only older speakers (like me) who have [ə]. So even in Britain, I am in the minority. We all have lots to learn in improving the clarity of our pronunciation.