Duplicacy doesn't seem to compress my files

Hello everyone,

I tried to find the answer to my questions but i didn’t find what i was looking for.
Everyone says that Duplicacy uses compression by default but that doesn’t seem to be the case for me. I use Duplicacy on docker (Hotio’s image) with the WebUI ( on a trial license, i want to resolve my issue before commiting to buy the license). For example when i backup a folder named “image” which is 20Go on my disk , it is also 20Go on the folder i choose to backup to. I know this is probably an error on my end but i can’t find any settings/info to solve my issue.

Anyone have any idea what is happening here ? thanks a lot !

Images are already compressed. They are not compressible any further. You can verify that by trying to compress them with any other compression tool like gzip, rar, xz, etc.

Thanks for the answer ! The command i did the check how much storage the backup folder was taking is du -h foldername. With that command it returns the same number of Go than the original folder. Is that normal then ? For context i ran all these command and the backup process on my headless linux server. i did the test on 2 different folder, one with 200Go size and the other 20Go size, same result both times : the backup folder is the same size as the original folder according to the “du” command. Again if you know where i failed in my setup i’m happy it :slight_smile:

I just tried with the executable version of duplicacy web GUI, the non docker one, and i have the same result, so i really don’t know what i’m doing wrong here. If anyone can give me any advice that would really help a lot ! thanks again :slight_smile:

Did you see my response above?

You are not doing anything wrong. Compression ratio depends on data being compressed. A 1GB file filled with zeros will compress with a million to one compression ratio, jpeg picture won’t compress at all, in fact, it will become larger.

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Ho sorry alright i didn’t correctrly understand your answer indeed. It’s also because i tried with 2 different folder and the second folder doesn’t really have much images in there but mainly documents and .iso files and that one also is almost the same size as the original folder. But i get it maybe it’s just that my files are already compressed. Thanks !

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Iso files are not themselves compressed – they contain the representation of original disk media as is, so compressibility depends on what’s contaned in those .iso files. For example, a software installation ISO might contain compressed installation files, and therefore be incompressible. Media .iso’s wont be compressible either. On the other hand an iso image of a disk containing old xls spreadsheets would be somewhat compressible.

Same here. My test is backing up folders of PDFs. The -zstd setting is reported in the log, but there doesn’t seem to be any compression.

Did you manage to resolve this?

You mean break laws of physics?

Modern PDF files are already compressed.

Take your PDF files and compress them with zip. Do you see size reduction?

Yes, I do see some compression of my PDFs with a simple zip. But not much.

But, I have looked more carefully at my logs - should have done that before! I have also added some folders with uncompressed text.

There is some compression with default zstd - but less than I would expect based on what a zip of a folder does.

So I withdraw saying there was no compression - glad you pulled me up. I will think about whether it is worth doing with my Duplicacy backups.