Use Case: Large File Transfer

Scenario

Transfer a single large file (e.g., 50GB VM image) across an air-gap using 16GB USB drives.

Use Case: Large File Transfer UC-TRANSFER-001

status: approved

tags: transfer, workflow, large-file, chunking

release: v1.0

specifies: FR-TRANSFER-001, FR-TRANSFER-003, FR-TRANSFER-005, FR-TRANSFER-007, FR-TRANSFER-009, FR-TRANSFER-010, FR-TRANSFER-020, FR-TRANSFER-031

Transfer a single large file (50GB VM image) across air-gap using multiple 16GB USB drives with automatic chunking.

Pack: Split file into chunks sized for USB capacity (one chunk per USB: 3x 16GB + 1x 2GB across 4 USB drives), generate checksums, create manifest on each USB.

Transfer: Physically move USB drives across air-gap boundary.

Unpack: Verify chunk checksums, reconstruct original file, verify final file integrity.

Acceptance Criteria: File reconstructed matches original, all checksums verified, no data loss, process completable by non-technical user.

Prerequisites

Source machine: Connected system with internet access
Destination machine: air-gapped system
Transfer media: Four 16GB USB drives
File: vm-image.qcow2 (50GB)

Workflow Steps

Phase 1: Pack on Source Machine

Connect USB drive #1

airgap-transfer pack vm-image.qcow2 /media/usb-drive --dry-run
Preview: Shows 4 chunks needed (3x 16GB + 1x 2GB)

Execute pack operation

airgap-transfer pack vm-image.qcow2 /media/usb-drive
Writes chunk_000.tar (16GB)

Generates SHA-256 checksum

Updates manifest

Swap USB drives

Tool prompts: “Insert next USB drive”

Eject USB #1 safely

Connect USB #2

Tool continues with chunk_001.tar

Repeat for remaining chunks

USB #3 contains chunk_002.tar (16GB)

USB #4 contains chunk_003.tar (2GB)

All USBs contain copy of manifest: airgap-transfer-manifest.json

Phase 2: Physical Transfer

Physically move USB drives across air-gap boundary
No network connectivity required

Phase 3: Unpack on Destination Machine

Connect USB drive #1

airgap-transfer list /media/usb-drive
Shows chunks present on this USB (chunk_000)

Connect all USB drives

Mount USB #1, #2, #3, #4

All chunks now accessible

Execute unpack operation

airgap-transfer unpack /media/usb-drives ~/restored/
Verifies checksums for all chunks

Reconstructs vm-image.qcow2

Verifies final file integrity

Reports: “Success: 50GB transferred, verified”

Acceptance Criteria

✅ File reconstructed matches original
✅ All checksums verified
✅ No data loss or corruption
✅ Process completable by non-technical user

Error Scenarios

Error	Cause	Recovery
“Chunk missing”	USB #2 not connected	Connect missing USB
“Checksum mismatch”	Corrupted chunk	Re-pack affected chunk
“Insufficient space”	Destination disk full	Free space, retry

Linked Requirements

ID	Title	Status	Release	Verified By
FR-TRANSFER-001	Split Files into Chunks	approved	v1.0	TC-PCK-001; TC-PCK-002
FR-TRANSFER-003	Generate Chunk Checksums	approved	v1.0	TC-PCK-004
FR-TRANSFER-005	Stream Data to USB	approved	v1.0	TC-PCK-006
FR-TRANSFER-007	Show Pack Progress	approved	v1.0	TC-PCK-008
FR-TRANSFER-009	Reconstruct Files from Chunks	approved	v1.0	TC-UNP-001
FR-TRANSFER-010	Verify Chunk Checksums Before Unpack	approved	v1.0	TC-UNP-002
FR-TRANSFER-020	Generate Checksums	approved	v1.0	TC-INT-001
FR-TRANSFER-031	Dry Run Flag	approved	v1.0	TC-TRANSFER-CLI-004

Traceability

Tests

Integration Tests

No needs passed the filters

Unit Tests of Linked Requirements

ID	Title	Status
TC-INT-001	Generate SHA-256 Checksums	approved
TC-PCK-001	Pack Single File into Chunks	approved
TC-PCK-002	Pack Directory into Chunks	approved
TC-PCK-004	Generate Chunk Checksums	approved
TC-PCK-006	Stream Without Temp Files	approved
TC-PCK-008	Progress Reporting	approved
TC-TRANSFER-CLI-004	Dry-Run Mode	approved
TC-UNP-001	Reconstruct Files from Chunks	approved
TC-UNP-002	Verify Chunk Checksums	approved