Practical File System Design Paperback – November 23, 1998

This book may be slightly over-sold on its jacket ("guide to the design and implementation of file systems in general ... covers all topics related to file systems") but that's likely not the author's fault. It does provide intermediate levels of detail regarding many, perhaps most, areas of concern to file system designers and deserves a place in the library of anyone embarking on such a project - though people expecting a cookbook rather than a source of detailed ideas will be disappointed.
The ideas are in general sound and representative of the current state of file system practice. The historical view is a bit Unix-centric - to state that the Berkeley Fast File System is the ancestor of most modern file systems is to ignore arguably superior and significantly earlier implementations from IBM, DEC, and others. This bias carries over into aspects of implementation as well, such as use of the Unix direct/indirect/double-indirect mapping mechanism to manage contiguous 'block runs' without adding file address information to the mapping blocks to eliminate the need to scan them sequentially (save for the double-indirect blocks, which avoid the scan by establishing a standard run-length of 4 blocks - arrgh!) when positioning within the file - and the unbalanced Unix-style tree itself would almost certainly be better implemented as a b-tree variant (with its root in-line in the i-node) indexed on file address. And the text occasionally blurs the distinction between what the BFS chose to implement (a journal system that forced meta-data update transactions to be serialized) and what is possible (a multi-threaded journal supporting concurrent transactions simply by allowing each transaction to submit a log record for each individual change it makes - which would also support staged execution of extremely large transactions eliminating the log size as a constraint on them).
Some of the choices made in BFS can be questioned, even in its particular use context. The 'allocation group' mechanism interacts in subtle ways with the basic file system block size, and given the relative and on-going improvement of disk seek time vs. rotational latency the value of locating related structures relatively near each other (though not actually adjacent) on disk may no longer justify the added complexity (though the effort to place file inodes immediately following the parent directory inode is likely worthwhile if a read-ahead facility exists to take advantage of it). The discussion of on-disk placement also ignores 'disks' that may in fact be composed of multiple striped units, which would further dilute the benefits of allocation groups; note that this would also complicate the read-ahead facility just mentioned, as would a shared-disk environment unless the disk unit itself performed the read-ahead and replication if present was taken into account (as in the Veritas file system, as I remember).
Even the fundamental decision to make attributes indexable deserves closer examination, given the costs of indexing. Current hardware can perform a complete inode scan on a single-user workstation fast enough to satisfy the occasional random query and can scan the inodes for files within some limited sub-tree of the directory structure (e.g., a cluster of e-mail directories) relatively quickly for more common queries, and in a multi-user environment indexing individual attributes across all users is frequently not the behavior desired. Placing index management under explicit application control may be a better approach, perhaps by allowing the application to specify on attribute creation the index, if any, in which its value should be entered (thus preserving the ability to encapsulate the operation within a system-controlled transaction without the need for user-level transaction support) - and storing the index (perhaps by its inode) with the attribute for later change or deletion.
Conspicuous by their omission are any mentions of how to manage very large allocation bit-maps (which one really must expect when other parts of the system are carefully crafted to handle 2**58-byte files) or the impact of a shared-disk environment (if BFS was intended to be limited to desk-top use this may be more understandable, but even desk-tops may soon have high-availability configurations). Security is mentioned briefly as a concern to be addressed later - but BFS's dynamic allocation of inodes from the general space pool makes this impossible, given that directory inode addresses can apparently be fed in from user-mode (the author does note this near the book's end, but fails to discuss possible remedies).
The author also expresses regret in the introduction at not having had time to include more comparative information on other file systems, both current and historical. Perhaps he is leaving himself room to write a second book. I hope so: despite my comments above, this one was worthwhile - both on its own merits, and because of the lack of competition in this subject area.

Great book for those who want to get into file system design, but don't know where to start. It's been out of print for a little while, but I contacted the author and he was happy to release a pdf of it on his website: [...] I would highly recommend it!

As other reviewers have pointed out, the author starts off by apologetically lamenting that he didn't have much time to go into very detailed analysis on other file systems. The author seems very knowledgeable in general, and it's a shame he didn't have more time to add some more breadth to the book. Some of my all-time favorite books are Patterson and Hennessey's two computer architecture books, because they are very dense with a wide range of well-explained ideas. This book is much less dense.
Perhaps the most annoying thing about this book though is that he doesn't finish his thoughts. I felt that often, just as he was getting to the interesting part after cutting through the fluffy descriptions of his design choices, he would leave the topic and not come back. The must frustrating part of this was that after skipping over many pertinent details of how he actually built the BeFS, he spends an excruciating amount of time describing the vnode layer and the exact API that the file system driver must write too -- something I feel would have been better left to a Be-specific API programming manual.
The editing could have used some help. Grammar and flow were pretty good, the book was readable. However, the author too often finished discussions by saying, "we didn't have time." This is annoying and gets old.
Also annoying was the repetion of some lines of thought unecessarily. For instance, he talks about B+ trees and then instead of finishing the conversation, wanders away and talks about something else, and then wanders back and repeats himself before continuing.
Overall organization was a little sloppy, with summary after summary of what was just discussed or what will be discussed next. Focus was also affected by the author's understandable tendency to spend too much time describing the minute details of this or that "tricky" implementation issue that he encountered while build his piece of the BeOS. Obviously he is proud of his accomplishments, and he should be, but I felt the subtle back-patting going on at various points in the book's explanations complicated them unnecessarily with testaments to the author's debugging and optimization skill, rather than providing a complete road-map and "beware" warnings to feature implementors. As I've already pointed out, the book doesn't have enough detail to implement something from, so it's kind of awkward for these very complete descriptions of certain types of problems to be present in the text.
I thought the "summary" sections at the end of the chapters were too creampuff to be useful -- I didn't pay for Cliffs' Notes in my book.
Overall, a reasonably worthwhile purchase, especially given the derth of material in this area, but there are more technical, better explained resources on the net that should also be consulted for more info about file system design.

I found this book a useful insight into the mechanisms at work in modern file systems. I especially found the performance comparisons of popular file systems useful, giving the reader the ability to analyze the trade-offs of the differing implementations, and how those design decisions are based on the requirements of the file-system.

I had wanted to buy this book for some time, butas a Unix Admin, I couldn't justify the money nor thestudy time. Well, now that I've bought it, I'mkicking myself for not doing so earlier. I havegained a much greater understanding of hashes, trees,filesystems, and databases. The book is an epitomeof clarity of thought and presentation. It's not often(never?) that I find a technical book that I wantto read cover to cover in one sitting! I only wishthat the author had more time to revisit the BeFSshort-comings that he mentions, and then GPL the endresult.