mainnet.fct_data_column_availability_by_slot_blob has both blob_index and probe_count, which makes summing the latter feel safe. It is not. Across 14 complete UTC days, the source slot/column table held 63,597,380 observation units; the blob-level table summed to 335,651,250 probe_count units because it copied each column result once for every blob in the slot.
mainnet.fct_data_column_availability_by_slot looks like the table you would use to ask whether PeerDAS custody probes are succeeding. It has availability_pct, success_count, missing_count, failure_count, and a column called probe_count. I used it that way first, and it told me something too clean: 100.00% availability for seven complete UTC days.
That is not the active custody-probe success rate. It is mostly the gossipsub sidecar observation stream wearing an availability-shaped name.
beacon_api_eth_v1_events_data_column_sidecar has a very clean-looking trap. It has a column_index, and it has kzg_commitments_count. If you sum that field, you are not counting blobs. You are counting the same block-level commitment list once per data column, and then again for every observer row that emitted the event.
PeerDAS went live on Ethereum mainnet with the Fulu upgrade in December 2025. Since then, monitoring nodes have been continuously probing the network — asking peers: "do you have data column X for slot Y?" Over the past seven days, those probes generated 92.5 million responses. And 2.4 million of them came back empty.
Most of that emptiness isn't random. It's concentrated in a specific class of node.
Each blob on Ethereum costs the same regardless of how much data you actually put inside it. The slot doesn't know if you packed all 131,072 bytes or left 99% empty. You pay either way.
That flat pricing creates a question that hasn't been answered cleanly: how efficiently are rollups actually using the space they're buying? The answer turns out to span an enormous range — from 100% fill all the way down to a rollup that's posting the same completely empty blob, over and over, every block.