> > Backblaze ships with 21 identical copies of the same executable
>
> This seems needlessly dismissive. I feel like they definitely know that you can execute the same binary multiple times.
I'm the programmer at Backblaze that made the copies on purpose, I wrote some extra code to do this, and it's meant to help us debug certain things. Yes they are identical, the installer only ships with one copy of the executable, the installer then makes the copies on purpose. I get to explain this from time to time. :-)
In Windows when you want to know what is going on behind the scenes, you can bring up Task Manager and look at the different names of the different processes that are running. On the Macintosh this is called Activity Monitor, same sort of thing. The different names for the executables are for different "threads" which have different roles. Backblaze is multi-threaded to get higher performance.
The parent coordination process is called "bztransmit". But when doing the actual transmission it spawns the bztrans_thread01, bztrans_thread02, bztrans_thread03, etc.
So BEFORE I made multiple copies of the executables with different names, a customer would say "bztransmit is hung" or "bztransmit is using up too much memory". There was very little visibility into this. But now that I made multiple copies with different executable names, when the same customer says "bztrans_thread03 is hung". Or they say "bztransmit is using too much memory". We immediately have narrowed down what to look at.
Here is a screenshot showing what "Chrome" looks like to me in Windows, and how it compares to how Backblaze's bztransmit looks like to me in Windows: https://i.imgur.com/KOJHJ9Q.jpg In that screenshot, you can see there is the "main thread", and "worker threads". Meanwhile chrome is just one big list of processes all named the same thing (see the screenshot). I prefer the Backblaze system, but I understand it upsets some customers that prefer the chrome experience.
That's it. It's not some huge mystery.
One question asked here was do we know you can launch the same executable twice? Yes, and we do that. The bztrans_thread05 is launched for thread 05, thread 25, thread 45, thread 65, etc. It's THREAD_NUMBER mod 20. Here is what it looks like to hit 500 Mbits/sec upload speeds, this isn't photoshopped, it's a real screenshot on my development computer: https://i.imgur.com/hthLZvZ.gif
Another question is: why not use hard links or symbolic links? That's the only real optimization possible here, everything else was on purpose. The answer is not an excuse, it's just an explanation if you are curious. The software we develop at Backblaze is cross platform, so what we like to do is make the most general form first that will always work, then if customers complain or we want to refine it we special purpose code in per file system or per platform. The most general thing to do is make full copies. We could then go on to make links on the Mac WHEN POSSIBLE and the equivalent on Windows WHEN POSSIBLE, but it never became a large priority. The reason I can't use one technology is we support several file systems, and not all of them are the same or support the same technology for links.
Every feature we have is the result of prioritizing it over working on other things. Until recently, we did not have a lot of funding or an infinite supply of programmers, so we had to choose what order to implement each feature in. I'm not saying we got all the priorities correct, or that we did things in the correct order. I don't really even think there is one correct order. For example, some individual home user customers prefer saving 180 MBytes of their valuable boot SSD space over me implementing single sign on for our corporate customers. On the other hand some corporate customers DEMANDED single sign on or they wouldn't purchase the product at all. They are both correct, but there is only one of me, so we made some judgement calls and left the multiple copies and worked on single sign on. Some customers were happy, some are miserable.
We do have open client recs for both Windows and Mac programmers, so if you would like to make a good salary, full benefits, and help us out, come join us! :-)