Data vs. Dayta

Data is technically the plural of datum, so, the “correct” pronunciation is dayta. This is also the most widely used pronunciation.

It is also pronounced Dah-tah in Australia and Boston area.
In modern non-scientific use it is generally not treated as a plural. Instead, it is treated as a mass noun, similar to a word like information, which takes a singular verb. So as long as you are not using it in a scientific context, it is usually fine to use “this data is”.
Strictly-speaking, data is a plural term. For example, if we are following the rules of grammar, we should not write "the data is" or "the data shows" but instead "the data are" or "the data show".

As usage has changed over time, Oxford Dictionary indicates both pronunciations are now acceptable.