Which sentence is correct?
I performed a reliability analysis.
or
I performed an reliability analysis.
Which sentence is correct?
I performed a reliability analysis.
or
I performed an reliability analysis.
Your first sentence is correct:
I performed a reliability analysis.
The choice between a and an has nothing to do with the noun. It is entirely dependent on the sound that comes after the indefinite article.
a whole hour.
a tropical island.
an honourable solider.
If the next word after the indefinite article starts with a consonant sound, the indefinite article needs to be a.
If the next word after the indefinite article starts with a vowel sound, the indefinite article needs to be an.
Whether or not use use "an" depends on the word that directly follows the article.
If the initial sound of that word is a vowel sound, we use "an." Otherwise, we use "a."
For your sentence, it would be
I performed a reliability test.
because "reliability" does not start with a vowel sound.
Whether you use a or an entirely depends on the word directly after the a/an.
An analysis
A reliability analysis
An accurate reliability analysis
etc.