backblaze b2 backup failed large file

TL;DR

B2 handles large files through its large file API with parts, and tools that try a single-shot upload, or pick part sizes outside B2 limits, fail exactly on the biggest files. Confirm the tool uses B2 large file support, set part sizes within B2 recommendations for your file sizes and memory, check the bucket and account for caps, and test with one large file before the full job.

backblaze b2 backup failed large file

Use this when

• Backups to B2 succeed for small files and fail on files over a few gigabytes.
• The tool log mentions large file, part, or maximum size errors.
• Uploads die near the end of a large file rather than at the start.

Not for this skill when

• All B2 uploads fail including small files. That is auth or connectivity.
• B2 returns rate or cap errors on every call. Account limits, different handling.

Steps

1. Confirm the largest failing file size and the tool B2 upload mode from its settings or logs. Verify: the failure threshold size is known
2. Enable the tool large file or multipart mode for B2 and set a part size inside B2 documented limits. Verify: settings match B2 guidance
3. Check the application key permissions include write on this bucket and the account has no restrictive caps hit. Verify: key scope and caps are confirmed
4. Upload one failing large file alone and monitor part progress to completion. Verify: the single file lands and its hash or size matches
5. Run the full backup job and verify the largest files are present in the bucket. Verify: the job completes with large files confirmed

Variant phrasings

backblaze b2 large file upload failed backup

The plain phrasing.

b2 backup fails big files part size

The part-size variant.

backblaze b2 maximum file size backup error

The limit wording.

Compatibility: Backblaze B2 Cloud Storage native and S3-compatible APIs, with backup tools supporting B2 large file uploads.

Why it happens

B2 splits uploads at a threshold: small files go in one call, large files must be started, uploaded in parts, and finished through the large file API. Tools with incomplete B2 support or S3-compatible paths that ignore B2 part rules break precisely at that boundary, which is why the failure tracks file size so cleanly.

Edge cases / pitfalls

• The S3-compatible endpoint and the native B2 API have different large file behaviours. Know which your tool uses.
• Unfinished large files hide in the bucket and count toward storage. Clean them in B2 console or API.
• Part size trades memory against part count limits. Mid-range values suit most backup tools.

Provenance

Resolved from the public thread: https://vectle.com/posts/pstG18SEYvy41hERAEr5HIyQ

Resolved from the public thread: https://vectle.com/posts/pstG18SEYvy41hERAEr5HIyQ

Thread query: backblaze b2 backup failed large file

TL;DR: B2 handles large files through its large file API with parts, and tools that try a single-shot upload, or pick part sizes outside B2 limits, fail exactly on the biggest files. Confirm the tool uses B2 large file support, set part sizes within B2 recommendations for your file sizes and memory, check the bucket and account for caps, and test with one large file before the full job.