Checksum Offload & DIT Data Speed Calculator
Calculate camera card offload duration, MD5 vs xxHash-64 checksum verification time, bus bottleneck throughput, and dual-destination safety copying across CFexpress, NVMe, and 10GbE network storage.
1. Source Media & Target Storage
2. Estimated Offload & Verification Duration
Understanding DIT Checksums, Bus Bottlenecks & The 3:2:1 Rule
On-set data management is the critical link between camera capture and post-production delivery:
- Why Drag-and-Drop is Forbidden: Operating system file copy dialogues (macOS Finder, Windows Explorer) do not verify data integrity bit-by-bit. If a memory cell drops a packet during transfer, corrupt video clips will only be discovered weeks later in the edit room. Professional DIT software (ShotPut Pro, Silverstack, DaVinci Resolve Clone Tool) uses cryptographic checksum hashes to verify 100% bit-accurate copies.
- MD5 vs. xxHash-64: MD5 was the historical film standard, but its calculation speed is limited to roughly 500 to 700 MB/s per CPU core, creating massive bottlenecks on high-speed NVMe drives. Modern productions use xxHash-64, which computes at over 15,000 MB/s (15 GB/s), eliminating CPU verification lag entirely.
- The 3:2:1 Backup Rule: Never format a camera card until footage exists in 3 copies across 2 different media types with at least 1 copy off-site.
Worked examples: copy time with and without verification
The tool works in two parts. The copy runs at the slower of the card's read speed and the destination's write speed, which is divided between the copies when more than one drive is written at once. The verification then reads every copy back at the slower of the destination and the hash algorithm, and adds to the total. The tool counts a gigabyte as 1,000 megabytes. The first table uses its starting settings of a 512 GB CFexpress Type B card, a Thunderbolt 4 drive and two simultaneous copies.
| Verification | Copy | Verify | Total |
|---|---|---|---|
| xxHash-64 | 6 min 6 sec | 6 min 6 sec | 12 min 11 sec |
| MD5 | 6 min 6 sec | 26 min 15 sec | 32 min 21 sec |
| SHA-256 | 6 min 6 sec | 48 min 46 sec | 54 min 51 sec |
| No verification | 6 min 6 sec | none | 6 min 6 sec |
The choice of hash decides most of the wait. With xxHash the verification costs as much as the copy, because the drive is the limit. MD5 is limited by the processor at 650 MB/s in the tool's model, so the same card takes more than two and a half times as long, and SHA-256 at 350 MB/s takes about four and a half times as long. The tool's dropdown describes MD5 as about 600 MB/s, and the calculation uses 650.
The second table holds the settings at xxHash with a single copy and changes the destination.
| Destination | Write speed | Copy | Verify | Total |
|---|---|---|---|---|
| Thunderbolt 4 NVMe SSD | 2,800 MB/s | 5 min 1 sec | 3 min 3 sec | 8 min 4 sec |
| USB 3.2 Gen 2 portable SSD | 1,050 MB/s | 8 min 8 sec | 8 min 8 sec | 16 min 15 sec |
| SATA 3 internal SSD | 500 MB/s | 17 min 4 sec | 17 min 4 sec | 34 min 8 sec |
| Single 7200 RPM external HDD | 140 MB/s | 60 min 57 sec | 60 min 57 sec | 121 min 54 sec |
The card stops being the limit once the destination is slower than the 1,700 MB/s the card reads. On the Thunderbolt drive the copy is held back by the card, and on the others the drive sets the pace. The slowest destination takes two hours for the same card, and half of that time is the drive reading the footage back to check it.
Working Vocabulary
Key DIT and digital storage engineering terms:
- Checksum Hash. A mathematical digital fingerprint calculated from the exact binary bytes of a file used to verify that copies are identical to the source.
- xxHash-64. An extremely fast non-cryptographic hash algorithm capable of saturating multi-gigabyte RAM buses during DIT offloads.
- DIT (Digital Imaging Technician). The camera department specialist responsible on-set for camera signal quality, live color LUT monitoring, and data offload integrity.
- MHL (Media Hash List). A standardized XML file format that stores file checksums, timestamps, and transfer logs for archival verification.