Hi @konidev20 ,

Thanks again for your time. This new method is working.

After some analysis, please consider this:
I really think that the original saveSmall and saveLarge functions are already there to differentiate PutBlob and PutBlock, considering the limits of the service Versions 2016-05-31 through 2019-07-07. But saveSmall do not use PutBlob in this implementation (maybe it was not implemented in the Azure SDK back then).

So maybe you just need to make some changes in azure.go:

• const saveLargeSize = 256 * 1024 * 1024 to const saveLargeSize = 5000 * 1024 * 1024 (line 44)
• Adapt saveSmall to use the correct Upload Azure SDK subfunction (for PutBlob API)
• buf := make([]byte, 100*1024*1024) to buf := make([]byte, 4000*1024*1024) into saveLarge function (line 299)

As you can see, values are matching the service versions table:

Also, it could be great to let the end user to choose the size (under the limits of course) with 2 options: (seems Rclone do it like that):

• A cut size option to choose when we want to use PutBlob / PutBlock,
  ie: -o azure.cutsize=512M would force to use PutBlob if file is under 512MiB, and PutBlock if over.
  This option can't be over 5000MiB (saveLargeSize variable)
• A chunk size option to choose how to split block via the PutBlock API,
  ie: -o azure.chunksize=16M would force 16MiB blocks via PutBlock API, so cumulated with the previous option, a pack file over 512MiB will be split into 16MiB blocks then a PutBlockList will be emitted to produce the whole file into the storage.
  This option can't be over 4000MiB.

This will ensure that anyone can set the values considering there needs and/or limits (seems that old Service Version of AzureStorage are still running. Also limits are not the same for the Emulator:

The Windows test failing in unrelated.

Also, it could be great to let the end user to choose the size (under the limits of course) with 2 options: (seems Rclone do it like that):
A cut size option to choose when we want to use PutBlob / PutBlock,
ie: -o azure.cutsize=512M would force to use PutBlob if file is under 512MiB, and PutBlock if over.
This option can't be over 5000MiB (saveLargeSize variable)
A chunk size option to choose how to split block via the PutBlock API,
ie: -o azure.chunksize=16M would force 16MiB blocks via PutBlock API, so cumulated with the previous option, a pack file over 512MiB will be split into 16MiB blocks then a PutBlockList will be emitted to produce the whole file into the storage.
This option can't be over 4000MiB.

@R23-Git
I think this would be a neat feature to implement in a new feature request maybe? To limit the scope of changes in this PR. This PR is essentially just replacing the implementation of the saveSmall function.

What would be the actual benefit of adding these options? Users already have the option to set the pack file size target via --pack-size. Almost all files created by restic remain near the pack file size target (currently limited to 128MB). While I plan to increase the pack file size in the future, it will never be larger than either 1 or 2 GB. In a few exceptional cases the pack files can be larger than that limit. But that isn't something we need an extra configuration option for.

According to https://learn.microsoft.com/en-us/rest/api/storageservices/versioning-for-the-azure-storage-services all regions use a 2025 version by now.

Keeping support for the emulator sounds reasonable though, so what about only cutting files into smaller parts that are larger than 2000MB?

I think this would be a neat feature to implement in a new feature request maybe?

I'm against adding this feature unless someone can provide a reason why it's actually necessary.

Let's keep the old blob size of 100MB for large uploads. Other than that the change looks fine.

I will need to update the docs and add a changelog. Will do that and mark this PR ready for review.

Thanks for the review!