Nevermind. Just read the release notes from v7.

Is there a plan to allow Synthetic fulls for Local backup accounts?

The suspect some of the difficulty with implementing that feature is that the API for network shares to manipulate the data is not ideal compared to cloud APIs. But I have asked the team for their thoughts - the request is already in the system. I'll report back when I know more.

Just completed a couple of tests of the V7 Synthetic full feature going to BackBlaze
VHDx file
Original Full (76GB) took 9 hours 5 mins (9:05) over a 1MB/s uplink.
Subsequent Synthetic Full took only 1:38 with 4GB of changed data uploaded.
82% reduction in runtime

Image
Original Full (72GB) = 8 hrs 26 mins
Synthetic Full - 8GB uploaded - Remainder copied in cloud = 2 Hrs 15 mins
73% reduction in runtime

The more data that has changed since the last backup , and thus has to be uploaded, the longer the synthetic will take, but regardless, this will dramatically reduce the backup time.
Hopefully we can now get all of our full backups completed over the weekend, rather than running for 3-4 days in some cases.

Thanks for your update Steve. Much appreciated.

Unfortunately there appears to be a problem with V7 and BackBlaze B2. We rolled out V7 to two clients whose VHDx/Images are so large that we could not complete the upload in a single weekend.
Both ran for a while but then halted with "Could not create SSL/TLS secure channel" errors.
I understand from support that this is a known issue, one which BackBlaze has provided little assistance in solving.
Apparently there is a workaround (developed by and available from Support) that we will test this week, but since it requires a server reboot (which requires approval from each client), it will slow our rollout significantly.

Question: Are there any BackBlaze transaction fees for in-cloud copying of data during a synthetic full?

That is significant reduction in time to create the synthetic full backup. I presume that this is when using the new backup format, is that correct?

Yes , I am using the new format. Synthetic fulls of Images and VHDx files take 75% less time as cooying data in the cloud is VERY fast.

Excellent!