Compression Level

[bilvihur]

Would you explain a little about Compression Level? I understand the higher the level, the greater the compression (and longer run time). What I'd like to know is what effect the Level increment has on common filetypes (PDF, MP3, MP4, AVI, etc.). For instance, using a 1GB MP4 file as an example, how large would the Archive file be using a Compression Level of 2, or 5, or 9, and how would the corresponding run time change? If you don't have this information handy, perhaps you can say what Compression algorithm Reflector uses, and I can read it's description. Thanks.

[cobian]

It uses the standard zip deflate algorithm. 9= Max compression, more time. 0-no compression at all, fastest.

[bilvihur]

Thanks for your response. I had just done a full backup to an old 500GB portable HD, and it took 29 hours at a compression level of 5! I did a little research based on your reply, and found this:
File types that are already compressed/badly compressible ( docx, ods, odt, pdf, avi, mkv, mpg, mp4, gif, png, jpg, mp3, wma, etc...) should probably be archived as is. It's a waste of time and CPU to try to compress them further.
The "sweet spot" for efficient Deflation of other file types is a compression level between 3 and 4, in terms of file size reduction and speed of operation.
I don't know about other users, but music, video, documents, and pictures constitute 90+% of the data I like to backup. Would it be possible to implement a list of file types for which no compression is attempted regardless of what the compression level is set to?
I hope this information is useful to you and others. Regards

[cobian]

You can add all extensions you want to store uncompressed in the settings.