Check -Chunks bandwidth usage

Been using Duplicacy for over a month now on Windows 10 with B2 cloud storage. No issues! I have been doing a “check -chunks” twice a week (Tue & Sat) along with a purge twice a week (Wed & Sun). I’m wondering how much data bandwidth on B2 I’m using by doing this check operation so often. My charge for bandwidth usage on B2 was higher than I expected.

I know Duplicacy keeps a list of verified chunks and only checks new ones.

Does it download the entire chunk? Isn’t this the same as downloading everything I have backed up since the last check? That would be a lot of bandwidth.

Am I understanding how much bandwidth is being used by the “check -chunks” operation correctly? Is it downloading all new chunks, or only a portion of those chunks (if that’s possible)?

I decided to change my schedule to do a “check” without the “-chunks” option and to do it only once a week. I figure just knowing the files are on B2 is good enough, I don’t need to download them.

I think duplicacy download every chunk that needs to be checked into memory and verifies them.

One way that I can think of to avoid downloading is like this:

First, backup to a local repository, but also add the B2 storage as ‘-bit-identical’.

Then using ‘duplicacy check —chunks’ on the local repository.

After it is verified, use ‘duplicacy copy’ from the local repository to the remote B2 storage in bit identical way.

In this way, there won’t be any download at all.

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-bit-identical is for a slightly different use-case (i.e. needed when using other methods to synchronise chunks). The main flag would be -copy to make it copy-compatible.

Either way, neither absolutely guarantees the uploaded chunks won’t get corrupted during or after copying to the remote storage, though I guess it’s a good way to check that at least one copy (your local one) is validated, since the process of copying chunks is like a check on the local side at least.


Thank you @jiahao_xu for the suggestion of using a local repo that is synced to B2 by another means. That is a good idea.

@Droolio - I thought the exact same thing as you - it’s nice to have the local copy of the repo that you know is not corrupted - but at the same time you still don’t know if the files uploaded to B2 got corrupted during the transfer or sometime later.

I was a CrashPlan customer (as a lot of us were) and when my grandfathered status and low cost expired about a year ago I started looking for a less expensive solution. I figure Duplicacy w/B2 will cost me about $2 a month or less. If it costs me $5 or $6 a month I might as well use Duplicacy w/OneDrive … because for that price I can get 1TB of storage and use of MS Office apps and basically unlimited “checks” and bandwidth to/from OneDrive.

So I’m trying to keep my B2 costs as low as possible.

If you already own a domain name, you can get free b2 download by setting up a custom domain: Using Backblaze B2 with the Cloudflare CDN – Backblaze Help, and then change the storage url to b2-custom://

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