Backblaze seemingly does not support files greater than 1 TB

For nearly a month now, Backblaze has been fixated on a particular file of mine, that happens to be over 1 TB in size. Backblaze seemingly uploads it completely, but then on the next backup it uploads it again, even though it has not changed (in eight years!). Ad infinitum.

Using their Explainfile tool to dig into the log files, the clue seems to be:

  - line 288 - 2024-12-16 16:16:17 0000000646 - ERROR: UpdateBzDoneRegardingFlsToBeExp - Z_B_TOO_MANY_CHUNKS bz_done_ line chunk related, numBytesInLargeFile=1099512156951, totNumChunks=104858, bz_done_line_is: 5	! …
  - line 522 - 2024-12-16 16:18:46 0000000646 - ERROR - bz_done_ INCONSISTENCY_FOUND - 20241216161846 - BadBadBadChunkRecord hexAsciiVal=0x78 - AfterBzdoneLargeFileAnalysis: chunkSeq=100001, highestChunkSeqSeen=104857, fileIdOfLargeFile=00000000002c53cd, dateTimeOfLargeFile=20231217091843, XYXBXXX_FILE_NAME: …

Admittedly I’m guessing somewhat, since that’s a rather reader-hostile log message, but the combination of the Z_B_TOO_MANY_CHUNKS error mnemonic and chunkSeq=100001 (because of its proximity to the arbitrary round number 100,000) strongly suggests that Backblaze is imposing a 100,000 chunk limit. Since chunks are 10 MB each, that’s exactly 1 TB.

This is unequivocally at odds with what they claim repeatedly on their website, on pages like What Backblaze Backs Up and File Sizes.

It’s not clear to me why this is suddenly a problem; is this a newly-imposed limit? It’s possible that a month ago I removed some exclusion on the file, but I don’t remembering doing that and I can see no reason why I would have excluded it to begin with. If it is newly imposed, that would imply it’s also retroactive – that Backblaze actually deleted the existing backup of the file from their servers, thus causing the client app to try uploading it again.

I reached out to their technical support, of course, but thus far have only received mindless responses – restart your computer, reinstall Backblaze, etc.

Update

I received no further response from Backblaze’s technical support. They asked me to send them the log files, which I did on January 2nd, 2025, and they never responded again.

As of this update (February 4th 2025) their website still falsely advertises support for files of any size.

Addendum

I was surprised to see that many folks on HackerNews were surprised by the idea of a 1 TiB file. I certainly agree that’s large, but it doesn’t seem unusual or inexplicable to me. In my case, this particular “problem” file is an encrypted, compressed disk image of the boot drive of a prior computer, that I saved when I upgraded to my current computer.

It’s true that I could probably throw it out at this point – it was just a precaution in case I forgot to migrate something over, so now (eight years later) it seems that either I made no such mistake or whatever I forgot to migrate doesn’t matter anyway. For now I’ve just manually excluded it from the backup, to work around Backblaze’s bugs.

There are other cases in which I’ve had files over 1 TiB, though – e.g. video files:

• With some cameras and recording modes (e.g. documentarian, interviews) it’s in principle easy to exceed 1 TiB per file. e.g. the Nikon Z9 & Z8 record around 700 MB/s for 8k60 N-RAW, which is about 24 minutes per TiB.
  
  Note that I don’t recall if I personally have ever actually exceeded 1 TiB this way. I mention it mainly for illustration. It’s also possible that the Z9 & Z8 shard large recordings into multiple files (I don’t recall seeing this in years – not since the 4 GiB per-file limit of cameras a decade ago – but perhaps I’ve just not had a single recording large enough).
• Usually (for me) it’s output files that are largest, since they can combine many clips. I use Final Cut Pro and its video compression capabilities aren’t great, so I export essentially lossless ProRes and then use ffmpeg or Handbrake for the real compression. ProRes 422 HQ is nearly a gigabyte per second for 8k60, so it takes less than twenty minutes of video to exceed 1 TiB. Fortunately these large intermediaries only have to live as long as the final compression takes (though that can be days, especially with the latest formats like AV1).