I have been using ASM for 2 years now on both RAC and single instance servers. I think I have a good handle on how to use ASM, but the documentation is extremely light on how ASM actually works and interacts with the RDBMS instance it is supporting. Things are improved a little with the 11g documentation, in that there is a new storage administrators guide book, but still it is not exactly clear on how ASM actually works.
I was therefore keen to get my hands on Oracle Automatic Storage Management which would hopefully give a better insight into how ASM works than is available via the documentation alone. Interesting to note that two of the authors are also two authors on the oracle documentation itself.
I would say it’s a bit hit and miss. The book starts with an introduction from the architect of ASM, Bill Bridge. This was fascinating, in how long it took to go from initial idea to released product, 7 years! I also found it interesting that part of the initial design goal was that there would not be a directory tree, and files would not have names nor be accessible via the standard OS utilities. It now makes sense as to why ASMCMD feels like a bolted on piece of crud. I wonder how much this lack of filesystem familiarity has hurt ASM take up? Certainly when first released I was skeptical, partly as I was so used to being able to “see” my database datafiles – it’s a bit of a mindset shift moving from a cooked filesystem. I’m still not all that convinced it brings much to a single instance, but I think ASM with RAC makes a lot of sense. The changes in name of the product over the years also give an amusing insight into marketing at Oracle.
Chapters 10, & 11 really give you the added value over and above the online Oracle documentation, in that they give more detail on how ASM actually works in terms of the metadata and how the RDBMS actually ineracts with ASM held datafiles. I found the myth-busting in these chapters very worthwhile. While Chapter 5 has a little on Allocation Units and extents that is also of use. Unfortunately, I would say quite a few of the Chapters have a bit of filler in them, and there are many screenshots. I’m not all that keen on screenshots and I personally find they take up a lot of space for little added value. I also felt a few of the chapters did not give much added value over the documentation, which to be fair does tell you what you need to get up and running with ASM.
So all in all, there are some nuggets in this title that I found interesting/useful to know, but I suspect you could bump along happily without it and if Oracle improved their documentation just ever so slightly, you could save yourself a good 30 pounds sterling.