Recent does not always equate to better, note. There are exercises in Bach that are still relevant today. Milenkovic's 1987 book has a fairly interesting angle on design that one does not find elsewhere.
And several comparative operating systems books do not have the wide range of case studies that such books used to have.
That said: There are some interesting books on Solaris and MacOS internals that I did not have (and indeed that did not exist) when that FGA was written. The Windows NT Internals book is now two books (parts 1 and 2) and on its 7th edition (with a slightly unfortunate cover design, per https://news.ycombinator.com/item?id=14321672). And of course there is a FreeBSD D&I book.
I've also bought an interesting old book on VMS internals, since then. It discusses ODS.
Have you ever checked out OSTEP: Three Easy Pieces? (http://pages.cs.wisc.edu/~remzi/OSTEP/) I am finding that a much more accessible, organized, and easy-to-ready resource than Tanenbaum's Modern Operating Systems. What do you think of it?
Also, I've recently got my hands on "Practical Filesystem Design," written by the developer of the BeOS filesystem. A PDF is available here: http://www.nobius.org/dbg/practical-file-system-design.pdf