Very large files

Where the file store supports it, files too large for one request go up in chunks: start the upload, append the chunks, finalize.

if (db.FileStoreSupportsMultipartUploads(venue.Photo)) {
    var uploadId = await db.InitiateMultipartUploadAsync(venue.Photo, "walkthrough.mp4");
    while (/* more data */) {
        await db.AppendMultipartUploadAsync(uploadId, buffer, length);   // strictly in order
    }
    FileValue value = await db.FinalizeMultipartUploadAsync(uploadId);
    // …or, on failure: await db.CancelMultipartUploadAsync(uploadId);
}

Append the chunks in order, one at a time. For speed, upload several files at once instead.
An upload lives in memory on that store. After 10 minutes without activity it expires and the partial file is deleted.
The node changes only when you finalize, so a cancelled or expired upload leaves it as it was.