Hello there,
Long story short: I have a big PC game collection from golden era (1995 - 2010) - digital ISOs and BINs and a limited space to preserve them. I dont trust clouds in any form, so I prefer old school external HDDs for store. For me 7Zip is a good way to archive them and save some space, but recently ive found out that if you convert a BIN or an ISO file to ECM and then you archive it with 7Zip (ultra compression), the final compression file size will be in most cases almost at a half compared to original non ECM file.
Example:
Original Bin file (rld-cl1.bin) - 672MB
Original Bin file zipped with 7zip on ultra compression (rld-cl1.7z) - 268MB
Original Bin file converted to ECM (rld-cl1.bin.ecm) - 586MB
Original Bin file converted to ECM zipped with 7zip on ultra compression (rld-cl1.bin.7z) - 195MB
So there is a difference of 73MB in this case.
Does this method is good? You can damage the BINs in any way if you ECM them, ZIP them, unzip them and UnECM them back to BIN? I noticed in properties of an UnECM(ed) BIN file that the BIN no longer have Last Modified Original Date - in this case was year 2005.
There are other different methods to save space? I dont care much about loading time from archiving/extracting. I just want to be sure that all the files remain untouched in this process. Thanks
you probably already have your answer in your post. if an archival copy of your data is desired, then any modification to the source is not good.
virtually any lossless archiver/compressor (bz, xz, 7z, etc) will give you back the bit for bit original. pre-processing the image with ECM may not - you decide if the small savings in storage is worth it. considering that ECM is a compression method and already compressed data is harder to re-compress… based on your results, I would say ECM is a lossy process as compared to the source - I have no way to confirm this, however, without looking at specs.
tl;dr: don’t lossy (potentially) pre-process data and meaningfully expect it to be considered a clean “archive”)
edit: clarification… my use of lossy here refers to the loss of (likely) redundant or non-useful data from the source. stripping this data may have zero functional effect on the recovered binary, but archival purists would likely be horrified ;-)
Thanks for your answer, yeah I m worried about that “Last Modified Original Date” thing. For now I will keep only 7z compression for storage, just to be sure. Maybe I will use the ECM method in the near future when I will be able to duplicate my files on a second backup drive(s).