Layered sugarcane farm

TangoTek's sugarcane design, rebuilt by Adil Gamez over 23 minutes. Each layer is a flat plan of ten dirt rows paired around five water channels, with an observer on every row watching the cane and a piston snapping it the moment it grows, and the water carrying everything out to the storage. Layers stack straight on top of each other and the video builds five. It is the largest and most involved of the sugarcane entries, and most of the trouble people report is lighting rather than redstone.

Light it before you finish it. jesse_boomera96 confirms 1.21.11 but says to put glowstone above the pistons, because the build is far darker in a real world than it looks in the video and mobs spawn inside.
BalkanSquad-u1o had mobs spawning on the dirt, picking up the sugarcane and then refusing to despawn. They switched to blue ice, which does not melt once the farm is lit.
Use packed ice or blue ice, never ordinary ice. ZCV7853 points out plain ice melts.
Pistons not firing is usually the cane, not the redstone. thesweetbliss breaks the sugarcane in front of the observer and replants it. themustachegamers4226 adds a repeater on both sides, and thesweetbliss warns never to run dust into the side of a repeater.
Shift right click the iron bars so they do not waterlog. TukituxOfc gives this as the fix when the water will not flow where it should.
Michael-qo5mj revives dead water by placing fresh source blocks over the existing water on each row, and thesweetbliss skips a source in every slot and drops the whole water system one block lower.