am I missing something

[Lego]

hello,Windows 7 - what I want is to periodically mirror of constantly changing folder to an external drive

one of the rules should be:
- overwrite L>R if L file changed it size (regardless of timestamp)

I set Compare to File Size but in Synchronization I can't find any Action concerning size
am I missing something?

(there is an action for Content and obviously if size changed content changed too but comparing content of all files in a ~1Tb folder would take forever)

[xCSxXenon]

Mirror will make destination look like source, no matter what. The only impact file size and timestamp have on a mirror is whether or not the destination needs to be updated

[Lego]

I don't know the internal working of FFS but from what I see there are different variants of Compare for the same Mirror mode, you imply that regardless of chosen variant, result would be the same

now, let say somebody would like to customize Mirror, which could be done very easy in the area of timestamp, but not in the area of size, I wonder why?

[xCSxXenon]

Again, when you are mirroring, timestamp/size are only relevant in determining whether or not the destination needs to be overwritten, added to, or deleted from. You can't 'customize' mirror because any change will make it not a mirror any more.

[Lego]

I understand the word MIRROR
if I want MIRROR then I would not look for program like FFS, clone disk or clone partition would do the job probably better,
the goal is to have control over it, call it as you will
as example:
let say I have collection of images where bigger is better (better resolution or less compression) and somehow one or more picture was overwritten by smaller inferior image of the same name with newer timestamp

MIRROR and the better image is lost
mirror with control over it would not overwrite the better picture if the rule "do not overwrite if the file is smaller" was set, it is still mirror for me
and that what I'm looking for regardless of the name of the operation

[xCSxXenon]

Gotcha, you are calling what you want a mirror but you don't actually want a mirror. No, there is no way to tell FFS to always prefer the larger of the two files in question.

[Lego]

thank you for clarifying my concerns regarding size in FFS

also thank you for the lecture about the MIRROR, now it would be a good time to lecture the owner of FFS and beg him to remove the timestamp "adjustments" because it is a big blow to the purity of the MIRROR