The Missing Gigabytes: Diagnosing Parameter Dependencies in a SNARK Proving Engine

In the lifecycle of building a complex distributed system, there comes a moment when the elegant abstractions of software architecture collide with the messy reality of production dependencies. Message 189 captures precisely such a moment in the development of cuzk, a pipelined SNARK proving daemon for Filecoin's Proof-of-Replication (PoRep) protocol. The message, a single bash command and its output, represents the culmination of a diagnostic thread that began with a failed proof and ended with the discovery of 88 gigabytes of misplaced cryptographic parameters. It is a study in how even the most carefully architected system can be derailed by something as mundane as a path resolution bug in a download tool.

The Context: A Proving Engine Without Its Proof

To understand message 189, one must first understand what cuzk is and why it matters. The Filecoin network requires storage providers to continuously generate Groth16 zero-knowledge proofs that they are correctly storing data. This proof generation, particularly the "C2" phase (the final Groth16 prover step), is extraordinarily compute-intensive, consuming approximately 200 GiB of peak memory and taking hours per sector. The cuzk project was conceived as a pipelined proving daemon that would orchestrate this work efficiently, managing multiple proof requests through a priority scheduler, caching expensive setup data (the SRS — Structured Reference String), and ultimately batching proofs across sectors.

By message 189, the team had just completed a significant milestone: the Phase 0 implementation of cuzk was operational. The gRPC pipeline had been validated end-to-end — a client submitted a 51 MB PoRep C1 proof request, the daemon deserialized it, dispatched it through the priority scheduler, and invoked the real seal_commit_phase2 function from the Filecoin proving stack. The proof itself failed, but it failed correctly: the error was propagated back to the client, and the Prometheus metrics accurately recorded the failure. The software architecture was sound.

The failure's root cause was simple: the machine lacked the 32 GiB Groth16 proving parameters. These parameters, which include the proving key and verification key for the Filecoin proof circuit, are massive files — the largest is a 45 GiB stacked-proof-of-replication parameter file. Without them, the prover cannot construct the proof. The immediate next step was to fetch these parameters using curio fetch-params 32GiB, a utility command that downloads the required files from a remote repository.

The Discovery: A Path Resolution Bug

Message 189 opens with the assistant's diagnosis of what went wrong during the parameter fetch:

The files were downloaded to ~/scrot/data/zk/params/ — but these are all just VK files (small, KB-sized) and a few small .params. The big 32G .params files (the ones starting with 8-8-2) are still missing — only the VK files were there from a prior download.

This sentence reveals the core problem. The curio fetch-params command was executed from the ~/scrot/ working directory. Due to a path resolution bug — or perhaps an intentional design choice that backfired — the downloader interpreted the target path /data/zk/params/ as a relative path rather than an absolute one. The files were written to ~/scrot/data/zk/params/ instead of /data/zk/params/. The assistant had already discovered this in earlier messages (185–188), noting the double slash in the log output (~/scrot//data/zk/params/) as a telltale sign of the path confusion.

But message 189 goes deeper. The assistant suspects that even in the wrong directory, the right files might not be present. The phrase "these are all just VK files (small, KB-sized)" indicates a preliminary check that revealed mostly verification key files — tiny cryptographic artifacts used for verification, not the multi-gigabyte proving parameters needed for proof generation. The assistant then executes a targeted investigation using three ls commands to determine exactly what .params files exist.

The Investigation: Reading the File System

The bash commands in message 189 are carefully structured to answer three specific questions:

What .params files exist? The first command lists all .params files in the ~/scrot/data/zk/params/ directory with human-readable sizes (ls -lh).
Are there any 8-8-2 parameter files? The second command greps for the pattern 8-8-2.*params$, which identifies the parameter files for 32 GiB sectors. In Filecoin's parameter naming convention, 8-8-2 encodes the sector configuration: 8 GiB nodes, 8 layers, 2 (the PoRep version identifier). The 32 GiB sector parameters use this pattern.
Are there any stacked-proof-of-replication files? The third command searches for the stacked.*8-8-2 pattern, looking specifically for the stacked proof of replication parameter file — the critical 45 GiB file needed for PoRep proof generation. The output reveals a mixed picture. Three .params files are present: - A 33 GiB file: v28-empty-sector-update-merkletree-poseidon_hasher-8-8-0-...params - A 57 GiB file: v28-proof-of-spacetime-fallback-merkletree-poseidon_hasher-8-8-0-...params - A 184 MiB file (truncated in the output) These are substantial files — 33 GiB and 57 GiB — but they are the 8-8-0 variants, not the 8-8-2 variants needed for 32 GiB sectors. The 8-8-0 parameters are used for older sector configurations or different proof types. The critical stacked-proof-of-replication-8-8-2 file is absent.

The Assumptions and Their Consequences

Several assumptions underpin the investigation in message 189, and understanding them reveals the reasoning process:

Assumption 1: The parameter files have a consistent naming convention. The assistant assumes that the 8-8-2 pattern is the correct identifier for 32 GiB sector parameters. This is a domain-specific piece of knowledge derived from the Filecoin proof system's parameter taxonomy. The naming convention encodes the sector size (8 GiB nodes), the number of layers in the Merkle tree (8), and a version identifier (2 for the current PoRep variant). This assumption proves correct — the subsequent message (190) confirms that the 8-8-0 files are the ones used for "PoRep 32G V1.1," an older version.

Assumption 2: The download completed successfully despite the path issue. The assistant assumes that the curio fetch-params command actually downloaded the files, just to the wrong location. This is a reasonable inference from the disk activity and the presence of large files in the wrong directory. However, the assistant also considers the possibility that the download was incomplete or that only VK files were fetched — hence the targeted check for the specific .params patterns.

Assumption 3: The missing files are the cause of the proof failure. This assumption is well-supported by the earlier end-to-end test, where the daemon successfully dispatched the proof request but the prover failed with a parameter-related error. The assistant is methodically working backward from the error to its root cause.

The Input Knowledge Required

To fully understand message 189, a reader needs several layers of domain knowledge:

Filecoin proof architecture: The reader must understand that Filecoin uses a multi-phase proof system where "C2" refers to the final Groth16 prover step. The proving parameters are large files (tens of gigabytes) that encode the circuit structure for a specific sector size and proof type.

Parameter naming conventions: The 8-8-2 and 8-8-0 patterns encode sector configuration parameters. The stacked-proof-of-replication prefix identifies the specific proof type. The v28 prefix indicates a version of the proof circuit.

The curio toolchain: The reader needs to know that curio fetch-params is a utility for downloading proving parameters, and that it has a path resolution bug that causes files to be downloaded relative to the current working directory rather than to an absolute path.

The cuzk architecture: The reader should understand that cuzk is a gRPC-based proving daemon that wraps the Filecoin proof stack, and that Phase 0 is the minimal implementation that validates the request/response cycle.

The Output Knowledge Created

Message 189 produces several concrete pieces of knowledge:

The parameter files exist but are in the wrong directory. The files were downloaded to ~/scrot/data/zk/params/ instead of /data/zk/params/.
The downloaded files are the 8-8-0 variants, not the 8-8-2 variants needed for 32 GiB sectors. This is a critical distinction — having the wrong parameter files is almost as bad as having none at all.
The largest file is 57 GiB, with another at 33 GiB. These sizes confirm that substantial data was transferred, but the specific files needed for the current proof type are absent.
The VK files (verification keys) are present but irrelevant for proof generation. The assistant notes that only "VK files (small, KB-sized)" were there from a prior download, indicating that previous parameter fetches had only retrieved verification artifacts.

The Thinking Process: A Detective Story

The reasoning visible in message 189 is that of a system detective working backward from a failure. The chain of inference proceeds as follows:

Observation: The proof failed with a parameter-related error.
Hypothesis: The required parameters are missing from the expected location (/data/zk/params/).
Test: Check /data/zk/params/ — confirmed empty (message 186).
New hypothesis: The curio fetch-params command downloaded files to a wrong location due to a path bug.
Test: Check ~/scrot/data/zk/params/ — files are present (message 188).
Refined hypothesis: But are they the right files? The initial check showed mostly VK files.
Test (message 189): List all .params files, grep for the specific patterns that identify 32 GiB sector parameters.
Conclusion: The files present are 8-8-0 variants, not 8-8-2. The critical stacked-proof-of-replication file is missing. This is classic diagnostic reasoning: each step narrows the hypothesis space by testing specific predictions. The assistant doesn't just check "are there files?" — they check "are there files matching the specific pattern required for this proof type?" This specificity is what makes the diagnosis effective.

The Broader Significance

Message 189 might appear, on its surface, to be a mundane file system inspection. But it represents a critical transition point in the cuzk project. The team had just proven that their software architecture was sound — the gRPC pipeline worked, the scheduler dispatched correctly, the error handling was robust. The final barrier to a fully successful proof was not a software bug but an environmental dependency: the presence of 88 GiB of cryptographic parameters on disk.

This transition — from validating software architecture to resolving environmental dependencies — is a universal pattern in systems engineering. Every distributed system, no matter how elegantly designed, eventually encounters the messy reality of deployment: missing files, wrong paths, incorrect versions, insufficient permissions. Message 189 is a microcosm of this struggle, showing how a path resolution bug in a download tool can block an entire proving pipeline.

The message also illustrates the importance of domain-specific diagnostic skills. The assistant doesn't just check for the existence of files; they check for files matching specific naming patterns (8-8-2, stacked.*8-8-2). This requires deep knowledge of the Filecoin parameter taxonomy — knowledge that is not documented in any single place but must be accumulated through experience with the system.

The Resolution

The story does not end with message 189. In the subsequent message (190), the assistant discovers that the downloaded files are actually the 8-8-0 variants, which are used for "PoRep 32G V1.1" — an older but compatible version. The critical 45 GiB stacked-proof-of-replication file is present after all, just with the wrong version number in its name. The assistant copies the files to the correct location (/data/zk/params/), and the environment is prepared for a successful proof run.

But message 189 remains the pivotal moment of discovery — the point at which the team realized that their problem was not a software bug but a path resolution issue compounded by a naming convention mismatch. It is a reminder that in complex systems, the difference between success and failure often comes down to knowing exactly which file to look for and where to find it.