The reason is simple: I have 2 big USB external HDs of a 1TB each, I am using it for a year in mirror without any problem, and even if they are less reliable than other drives, it works fine for me and I only want to be able to shut down the system ignoring any error at the end of the shutdown procedure so that I can reboot the system without having to go phisically to the computer and push a reset bottom. This is the only problem I am having and cannot find a solution anywhere.
The problems you are experiencing aren't FreeNAS issues. They really are issues with the administrator(no offense). No administrator in their right mind would or should be using USB as permanent storage. FreeNAS shouldn't be coded to ignore errors unless those errors don't matter. For everyone else, the problems you are seeing could be serious problems because we didn't use USB. But your configuration is non-standard, hence your problems. If I were having your problems, I'd know something was seriously wrong and go investigating. So either its coded so that the 99.9% of us that do things correctly don't get appropriate error messages and responses from the system or the .1% of users that are doing things that shouldn't be done anyway are inconvenienced. I'd prefer that only that .1% be inconvenienced.
I am pretty sure I am not the only one using big external USB drives and such a great system as FreeNAS should be able to shut down, but it does not. Running Ubuntu on a USB, on the same machine with the same HW, it shuts down without any problem and this is therefore clearly a SW error and if Ubuntu works, I would expect and like FreeNAS also to be able to shut down, that is all.
You are absolutely right that you are not the only one using external USB drives. Plenty of other people have too. And if you search around you'll see that
many of them have lost their
entire pools because they used USB. Also, Ubuntu(which is a flavor of linux) is not FreeNAS(which is based on FreeBSD which is more like unix). These are totally different OSes. What works in Windows doesn't always work in Linux. So why you'd expect that what works in Ubuntu clearly should work in FreeNAS is somewhat confusing and beyond me.
And just like with linux, many drivers in FreeBSD are written because people hacked together a driver that worked "good enough". And quite often manufacturers change their specifications, motherboards customize some onboard hardware, and sometimes the hacked drivers don't work well enough. If manufacturers choose not to make a FreeBSD driver for your hardware then you either:
1. Buy appropriate hardware from companies that do support FreeBSD and its drivers.
2. Accept that stuff may be broken or not work at all.