Do you need to know about GEOM? It's in here: Lucas takes your from "What *is* GEOM, anyway?" (answer: FreeBSD's system of layers for filesytem management) through "How do I set up RAID 10?" through "Here's how to configure things to solve that weird edge-case." Still trying to figure out GUID partitions? I sure was...and then I read Chapter Two. Do you remember disklabels fondly, and wonder whatever happened to them? They're still around, but mainly on embedded systems that still use MBR partitions — so grab this book if you need to deal with them.The discussion of SMART disk monitoring is one of the best introductions to this subject I've ever read, and should serve *any* sysadmin well, no matter what OS they're dealing with; I plan on keeping it around for reference until we no longer use hard drives. RAID is covered, of course, but so are more complex setups — as well as UFS recovery and repair for when you run into trouble.Disk encryption gets three chapters (!) full of details on the two methods in FreeBSD, GBDE and GELI. But just as important, Lucas outlines why disk encryption might *not* be the right choice: recovering data can be difficult or impossible, it might get you unwanted attention from adversaries, and it will *not* protect you against, say, an adversary who can put a keylogger on your laptop. If it still make sense to encrypt your hard drive, you'll have the knowledge you need to do the job right.I said that this covers *almost* everything you need to know, and the big omission here is ZFS. It shows up, but only occasionally and mostly in contrast to other filesystem choices. For example, there's an excellent discussion of why you might want to use FreeBSD's plain UFS filesystem instead of all-singing, all-dancing ZFS. (Answer: modest CPU or RAM, or a need to do things in ways that don't fit in with ZFS, make UFS an excellent choice.) I would have loved to see ZFS covered here — but honestly, that would be a book of its own, and I look forward to seeing one from Lucas someday; when that day comes, it will be a great companion to this book, and I'll have Christmas gifts for all my fellow sysadmins.One big part of the appeal of this book (and Lucas' writing in general) is that he is clear about the tradeoffs that come with picking one solution over another. He shows you where the sharp edges are, and leaves you well-placed to make the final decision yourself. Whether it's GBDE versus GELI for disk encryption, or what might bite you when enabling soft updates journaling, he makes sure you know what you're getting into. He makes recommendations, but always tells you their limits.There's also Lucas' usual mastery of writing; well-written explanations with liberal dollops of geek humor that don't distract from the knowledge he's dropping. He's clear, he's thorough, and he's interesting — and that's an amazing thing to say about a book on filesystems.Finally, the technical review was done by Poul Henning-Kamp; he's a FreeBSD developer who wrote huge parts of the GEOM and GBDE systems mentioned above. That gives me a lot of warm fuzzies about the accuracy of this book.If you're a FreeBSD (or Linux, or Unix) sysadmin, then you need this book; it has a *lot* of hard-won knowledge, and will save your butt more than you'll be comfortable admitting.You can purchase FreeBSD Mastery: Storage Essentials from amazon.com . Slashdot welcomes readers' book reviews (sci-fi included) -- to see your own review here, read the book review guidelines , then visit the submission page . If you'd like to see what books we have available from our review library please let us know