Syncing cloud storage with external hard drive

Question

I basically want to have a clone of my External HDD uploaded to a cloud service. I need a way to execute a 2-way sync every time the External HDD is plugged in. So, the changes made to the cloud (new files or deleted files) would reflect on the External HDD and vice-versa.

I'm on a macOS Sierra and need 1TB of cloud storage.

For cloud storage I'm planning to use one of those:

• Backblaze B2
• pCloud
• Amazon Cloud Drive

Question: Is there a software tool to do that?

It seems like a simple task, but I couldn't find any reliable way to make it work.

The solutions I have tried so far, without success:

Cyberduck Synchronise function

Not reliable. It tends to always add missing files. I.e.: If I delete a file from the cloud storage, the Synchronise function will re-upload the file back to the cloud storage instead of deleting it from the External HDD.

pCloud app

The sync process doesn't start when I plug my External HDD back in. I make changes to the cloud storage, the app tells me it needs to sync with the External HDD, but the sync never starts. No matter what I do.

odrive

Seems like it would do the job, but at $8/month it's prohibitive. I'd rather do it manually.

UPDATE 13 Mar

I tried a couple of other options without much success and here's the breakdown.

Arq backup

Really good and simple software, but mainly focused on backup, so it doesn't offer sync.

Carbon Copy Cloner

Great for what it does. It doesn't offer cloud integration. I tried to duplicate a folder using a mounted webdav volume, but it turned out to be too unreliable and failed to copy many files.

Acronis True Image

Super fast data transfers (in EU), unfortunately no sync on the mac app. Also doesn't offer acess to their cloud using WebDAV, SFTP or any other protocol making it a closed system to their app.

GoodSync/ Duplicacy / Syncovery / Duplicati

In theory these apps would get the job done, they promise to sync a cloud service to a local volume. But all of them have a very clumsy interface that put me off. They look outdated and don't fit the macOS UX. Some of them depend on external framework like .NET or Mono.

Answer 1

I've been doing initial tests with pCloud for this use case. I store my Lightroom catalog on an external HD that I want to backup to the cloud using their lifetime 2TB plan.

pCloud recently added backup functionality in addition to the existing sync. It's not clear to me what exactly the difference between these two is, because the backup configurations also perform two-way syncing. Their FAQ mentions that syncing files from external HDs is not recommended. I asked them on Twitter whether the same goes for backup, but I didn't get a useful reply (at least not yet).

Testing with a single directory on an external USB HD seems to work well. Unmounting and plugging in the drive again doesn't seem to break synchronization like you described.