Size of merged file larger than sum of constituent file sizes

Dear experts,

When merging several root files using “hadd” I noticed something which seemed a bit odd to me, namely the size of the merged file being more than twice as large as the sum of the sizes of all its constituent files. The command I used is basically:

“hadd merged.root someDirectory/*root”

and in my case the sum of the sizes of all root files in the directory I want to merge is 9 GB, and the merged file has a size of 22GB. Is this behavior normal or does it mean I am somehow doing something wrong?

Thanks for the help!



Hi Willem,
first of all, why do you need to make a huge file, this might slow down your analysis.
I guess something went wrong, normally the new file is less than the original files.
Maybe the compression changed?

hadd -ff ...

You could also try other compression levels. But -ff is usually what you want.

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