Is it fine to post my paper's preprint both on my blog and on arXiv? There is no particular reason that I want my preprint paper both on my blog and on arXiv, but I just thought it would look nice on my blog. If I were to do this, will arXiv mark my paper as plagiarized, because there is another copy on my blog? If so, how do I prevent this (is there an option to fill-in alternate links to the same paper)?

The following concerns me:


I have heard that arXiv have their own moderators, so that lead me to assume they might have a plagiarism test done on submitted papers. If my paper is already on my blog, isn't it more likely to be flagged as plagiarized by any average plagiarism software?
I have been surfing the web to understand about arXiv: https://www.reddit.com/r/AskAcademia/comments/5dq2jx/what_does_it_mean_to_have_your_paper_rejected_by/ There have been evidences of proper articles being rejected. This being the case, how does it ensure security?
The reason we post our papers first on arXiv is to prevent the content from being stolen by some anonymous person, who first rejects our paper upon submission and unlawfully uses the content elsewhere. How is arXiv different in this aspect? 


I haven't used arXiv before, and this is going to be my first time and I apologize if my question is very basic, I don't have much experience with these stuff.
If my paper is already on my blog, isn't it more likely to be flagged as plagiarized by any average plagiarism software?


This won't be a problem, unless you do something really weird, like post your paper on the blog under a different name.  Lots of arXiv papers also appear elsewhere, and the arXiv couldn't function if this caused trouble.


  There have been evidences of proper articles being rejected. This being the case, how does it ensure security?


I'm not sure I understand what you mean by security.  Strictly speaking, nothing is ensured, but in practice I believe very few proper submissions are rejected (almost none).  Unless you are an amateur researcher or are working on something unconventional, I don't think you need to worry about rejection by the arXiv.


  The reason we post our papers first on arXiv is to prevent the content from being stolen by some anonymous person, who first rejects our paper upon submission and unlawfully uses the content elsewhere. How is arXiv different in this aspect?


It's not different in principle, but in practice I don't consider this a serious issue.  I doubt any arXiv moderator has ever stolen a submission, since the risk/reward ratio would be terrible.  (It makes little sense to try to steal a paper when the authors will presumably post it online somewhere else shortly, and when there's an electronic record that you rejected it from the arXiv.)

More generally, I disagree that this is a key reason to post to the arXiv, since theft by reviewers is rare.  When people talk about establishing credit by posting to the arXiv, they generally aren't talking about preventing theft, but rather publicizing the work enough that nobody else will independently make the same discovery and claim credit.