>>...each of this sub-folders have 25 thousand files and around 130 Gb, and we do not
>>notice any slow down... except when we run 7Zip for the folders that are more than a
>>year old... that takes around 36 hours to run!
>
>
>We did some testing recently on 7-Zip on a directory tree (main, plus two sub-directories) of mostly DBF, FPT, and CDX files.
>
>

Using these levels for compression, 303 files, 375 MB, compressed down to:
>1 = 4s, 19.9MB
>3 = 4s, 19.9MB
>5 = 59s, 16.4MB
>7 = 82s, 15.5MB
>9 = 180s, 14.8MB
>

>
>If storage space is not the primary concern, switching to a compression of 3 yields 15x to 45x better performance for at most a drop of 25% in storage space. It might even be worth compressing using 3, then to recompress the smaller file using a higher value.

I am actually waiting to know what do they want to do with the data, we will probably end up moving the data, uncompressed for immediate use, to a large RAID and then delete the files older than 5 or maybe more years, but this decision is taking long to be made, so in the meanwhile the 2 TB disk that I am using is getting full, so I use 7-Zip with a compression ratio of 7% which leaves us with a 8-10 Mb 7z file at the expense of long processing time.

I did not think about using a worse compression ratio and then re-compress, maybe I'll try that next week (as I am already running one that will finish in 28 hours and I do not want to slow it down)