Octave mandola pentatonic scales
Four five-note shapes in GDAE tuning, all in first position. Almost everything written about banjo pentatonics assumes a five-string tuned to an open chord; these charts are drawn for fifths.
G major pentatonic
The five safest notes in the home key of Irish music. Drop the C and the F sharp from G major and every note left sounds good over every chord in a G tune.
E minor pentatonic
The same five notes as G major pentatonic, centred on E. The first shape most string players ever learn, and it works over the whole E minor and E dorian family.
D major pentatonic
D major minus the G and the C sharp. Useful in the other home key, and the shape is one string over from G major pentatonic.
A minor pentatonic
The blues-and-folk workhorse, relative of C major. Over A minor and A dorian tunes it never lands on a wrong note.
When these actually help in Irish music
Irish tunes are not pentatonic: they live in full seven-note scales and modes, and the melody is the point. Where the five-note shapes earn their keep is at a session with a tune you half know - every note in the shape is safe over every chord in the key, so you can shadow the melody without landing on a clash. Once a tune is under your fingers, move to its full scale: the two "missing" notes are usually the ones that give a tune its character.
Questions about pentatonics
A five-note scale: the major pentatonic drops the fourth and seventh notes of the major scale, the minor pentatonic drops the second and sixth of the minor. The two dropped notes are the ones most likely to clash against a chord, which is why every note left always sounds safe. On GDAE tuning all four shapes sit in first position.
G, A, B, D and E. Drop the C and the F sharp from the G major scale and they are what remains. E minor pentatonic is the same five notes centred on E.
Mostly no: Irish tunes use full seven-note scales and modes, and session players improvise inside the tune's own scale rather than a pentatonic box. Some of the oldest airs lean pentatonic, and the shapes are genuinely useful as safe notes over a tune you half know - but treat them as training wheels here, not the destination.
No. Five-string banjo is tuned to an open G chord and nearly everything written about "banjo pentatonic scales" assumes it. GDAE tuning is fifths, like a fiddle, so the shapes on this page are drawn for the instrument you are actually holding.