I don't know if it is a true Irish Chain - I see three types of blocks used in the overall block.
4 patch / 9 patch / 1 patch / 9 patch / 4 patch
9 patch / 4 patch / 9 patch / 4 patch / 9 patch
1 patch / 9 patch / 1 patch / 9 patch / 1 patch
9 patch / 4 patch / 9 patch / 4 patch / 9 patch
4 patch / 9 patch / 1 patch / 9 patch / 4 patch
If the finished block is 30 inches across, then each individual block measures 6 inches (6.5 with seam allowance).
So the solid 1 patch blocks (4 light, 1 dark) - finish 6 by 6 and are cut 6.5 by 6.5
The four patch blocks finish 3 x 3 are made from 3.5 by 3.5 inch pieces (I would strip piece with 3.5 inch strips)
The 9 patch block are made of 2x2 squares - strip piecing, I would cut the strips at 2.5 inches with the seam allowance.
Hope this helps.
K