I am reconsidering my "best practices" for Archival Blu-ray ROMs and looking for expert advice regarding filesystem structure.
Currently, I use Roxio Toast's "Mac & PC" setting. This creates a "Hybrid" disc containing both HFS+ and ISO 9660 with extensions. Great for Mac and seems to work well in Windows even with very large files and complex filenames, but I have not tested extensively. Unfortunately, I can't find solid documentation on precisely what ISO 9660 extensions Toast is using.
Is this indeed as good a choice as any or are there hidden pitfalls?
Is there a problem with the presence of HFS+ on the disc?
Would UDF be safer than ISO 9660 using "multi-extent" tricks?
Should I look for a way to use all three: HFS+ and UDF and ISO 9660?
A hybrid HFS+ plus UDF does not appear to be an option with Toast, though it might be possible with something else, like burn. In Roxio for Windows, the defaults for cross platform BDr seem to be ISO 9660 + Joliet + UDF (version not specified). Windows systems can't write HFS+ so the Toast style hybrid is not an option.
Having worked with all of those formats, I believe that using the Mac + Windows setting in Toast really is the safest and most compatible way to do what you're trying to do. You'll also find that setting allows you to access the content on other platforms like Linux and Solaris.
However, since you're probably not dealing with modern files that still have resource forks attached, you could save yourself some time and space by choosing just the ISO9660+ format since Mac's can read those as well.
It's an easy enough thing to test, so I build a Windows / ISO 9660 burn and see what you think.