Customer Reviews

Managing Raid on Linux

5 star:		(2)
4 star:		(0)
3 star:		(3)
2 star:		(4)
1 star:		(1)

 

 

I agree with all of the other reviews except the one that gave this book 5 stars! One of the most important topics that this book should have covered is how to recover from a disaster! How to replace a hard drive and re-sync the data to the new hard drive.

GURB is now an important boot loader and it doesn't even talk about it! Did you know that if you mirror (RAID 1) your drives during install and use GRUB as your boot loader your second disk won't boot if the first disk fails?

GURB doesn't copy the boot sector to the second (mirrored) disk during the RAID setup! You will be laboring under the mistaken thought that you will be ready *when* your system fails. What you don't know is that it is VERY hard to find out how to copy the boot sector to drive #2 using GURB. I still haven't found out after weeks of searching and posting in newsgroups.

If you can't recover from a failed drive, then you may as well NOT have a RAIDed system cause it wont do you any good. I can't believe that this book would leave a topic like that out! Just my two cents.

The availability of HOW-TOs and newsgroups is supposed to make the sysadmin's job easier, right? Much as I am a proponent of the 'distributed learning model' for Linux, the endless searching for answers on the Web for setting up Linux RAID was getting to be a royal pain. Sure, there was a RAID how-to and an excellent newgroup, but some of the information is out of date, and the tricks suggested by people a year ago may be no longer needed today.

A person deciding to go with RAID faces a panoply of options and
gotchas. Hardware or software? How many controllers? ATA or CSI (or ataraid)? RAID 1 or RAID 5? Which file system or disstribution? Kernel options? Mdadm or raidtools? /swap or /boot on raid? Hybrid? Left or right symmetric? One poster pointed out that putting two ATA drives on the same controller could impact performance. Yikes! Didn't I do that?

Upon discovering that O'Reilly had just published its Managing RAID on Linux book, looking at sample chapter , I bought the book and let my blood pressure return to normal.

RAID is one of these subjects that is really not complex; it's just very hard to find all the information in one place. This is precisely the book to solve the problem. Author Derek Vadala, sysadmin and founder of Azurance, an open source/security consulting firm, has gathered a lot of information and even personal anecdotes to go through the decision making process when going over to RAID. He goes
step-by-step through that process, educating us about hard drives, controllers, and bottlenecks along the way. This exhaustive book may be the first to bring RAID to the masses.

Although parts of the book (RAID types, file system types) may seem already familiar to experienced Linux users, it is helpful nonetheless to have everything in a nifty little book. A section of file systems provided not only a rundown of the merits and drawbacks of each one, but also a guide to their utilities. I learned for example what "file tails" for Reiser are, and why using them causes performance to degrade after reaching 85% capacity. The book compares raidtools with
mdadm as well as lovely commands to email you RAID status reports upon boot).

People who use software RAID may skip over the chapter on RAID
utilities for the leading RAID controller cards. Still, there was one interesting tidbit: Why, the author asks, do makers of controller cards put all their BIOS utilities on DOS floppies which require us to find a DOS boot disk? Seriously, how many of us carry around DOS boot disks nowadays? The book made me aware for the first time of freedos, an open source solution that solves precisely that problem.

The Software RAID stuff was pretty thorough and clarified a lot of things. The book does an excellent job in helping to identify and eliminate bottlenecks and optimizing hard drive performance (using hdparm and various monitoring commands). The anecdotes and case studies definitely clarified which RAID solution is suited for which task.

I am less impressed by the book's sections on disaster recovery and troubleshooting. Although these subjects are brought up at several places in the software RAID chapter, the book could have discussed several failure scenarios or used a fault tree (such as the famous Fault Tree in Chapter 9 of the Samba book, a marvel for any tech writer to read). The book doesn't even discuss booting with software RAID until the last 10 page of the book and then gives it only a single paragraph (even though the author acknowledges it as "one of the most frequently asked questions on the linux-raid mailing list."). Call me old-fashioned, but isn't the ability to boot into your RAID
system ... kinda important? As someone who just spent a significant amount of time troubleshooting RAID booting problems in Gentoo, I for one would have liked more insight into the grub/lilo thing. Also, in the next paragraph in the last chapter on page 228, the author casually mentions that "all /boot and / partitions must be on a RAID-1." Say what? Please pity the poor newbie who religiously follows
the instructions in the book but fails to read until the end. I'm not sure what the author meant by this statement, but it required a much more substantial explanation and needed to go into a much earlier chapter.

These complaints don't detract very much from this excellent book, a true O'Reilly classic and a model of clarity and helpfulness. This book provides enough knowledge to avoid the dread and uncertainty that comes with trying to tackle Linux RAID. With a book like this, a sysadmin can sleep a little easier.

I was pretty diappointed by the content of that book.
The graphs and the explanations on what is RAID are nice, but there are only a few lines about what to do if something goes wrong, which is the kind of situation you would like to have a strong reference on how to save your data.

I would rate this book as ok for beginners, but when you want to know more, you don't have much help, so a bad mark for advanced users.
I expected a more advanced work like on the O'Reilly book 'Using Samba' which is very nice, especially the Troubleshooting section.

I have to echo Lamar Thomas's review -- there is precious little on how to recover from a failed drive. You will have to go back to Google to learn how to recover from a single failed disk if using software raid to provide redundancy for your data. Having a paper reference for various types of disk recovery (in the case of not having a readily available web browser at the same site as the raid server machine) was the main reason I bought this book. So I was quite disappointed. Most of the book's material on hardware raid controllers is dated and by nature vendor specific. Moreover much of the material on creation of software raid that this book provides is unnecessary if one creates the raid partitions at installation.

The first 60 pages of this book read like an A+ guide to disk systems, and while that might be useful to some people, a topic like managing RAID on Linux is not the place for it. I'm guessing that if you are interested in this book you already know the difference between SCSI and IDE and really don't need someone to tell you the maximum length of an IDE cable.

While the author mentions disk failures we only get 5 short paragraphs on how to go about recovering. The rest of the book is devoted to describing the tools you can use to manage, build, and tear down arrays with equal time given to the earliest (outdated) RAID implementations. I found good and interesting data on approximately 20 of the 250 pages in this book, which means that this will probably replace sendmail as the worst O'Reilly book of all time.

What this book does really well is aggregate info that is available on the net, so if you don't have an internet connection or are too lazy to spend the two hours it would take you to google this data up, go ahead and order it

Description

Some 230 pages that read easily. The first two chapters explain what RAID and the RAID levels are, what Linux offers, and compares software to hardware implementations. The third chapter gives detailed instructions on how to build a software RAID, using mdtools or mdadm. It tells you how to build the kernel with the right options, which may be unnecessary for you. There's some history of versions of the kernel, raidtools, mdadm. Furthermore, we get detailed information about creating arrays by hand, including hybrid arrays for combining the benefits of different RAID levels. The forth chapter gives a detailed reference about mdtools and mdadm, and the /proc pseudo-files provided by Linux. The fifth chapter presents some general issues of hardware RAIDs, and then goes into detail of five specific products. The sixth chapter is not about RAID at all: it gives an overview of the Linux filesystems. The last chapter is a mix containing managing RAIDs, configuring hard disks, performance, and booting. The book is rounded off by literature abd internet references. The book uses kernel 2.4.

Comment

By now we know that Linux is important. Linux software RAID comes for free and is fairly good. Therefore the book is justified. The book gives a good introduction explaining the RAID levels. The discussion about ATA versus SCSI is good. The comparison is an important complementary topic. The comparison between software and hardware implementations of RAID is good, too. The author expresses his opinion. I like my author to have an opinion. Vadala argues the case of software RAID in Linux. The material about filesystem discussion is okay, but not necessary here. As others have also noted, some topics must come earlier and clearer. For example a discussion of boot loaders. The material about fault detection and correction could be improved. On the whole, the book could be more problem-oriented.

Who should read it?

To set up a RAID, there's not much secret and the book will give you some added detail, but no big surprises. If you are a home user you probably don't need this book, although you might be curious. If you are a system admin, the book is useful as it resumes the tools necessary to create and manage RAIDs by hand and contains much information in gathered, well-presented form. Most of the information is available on the net.

The book covers RAID and storage concepts on Linux systems. The book covers a lot of RAID concepts which are typically not covered collectively in sysadmin books or certification exams.

This book is great especially if you're a non-Unix systems administrator responsible for some Linux machines. The reference chapters themselves are worthy of 'keep handy' status in the admin's collection.

If you're interested in strict network or vendor storage technology such as SANs then this book is not for you. However, beneath the SAN and other storage network concepts lie the tried-and-true RAID techonolgies. One only has to look at current network appliance vendors to see that Linux is well suited to handle RAID on their products.

"Managing RAID on Linux" by Derek Vadala is a great intro and reference for understanding and setting up your own Linux RAID system at home or at work. The book does a great job of defining the terminology, covering the various RAID levels and explaining the technology. It covers both software as well as hardware RAID solutions, planning and tuning. The chapter on file systems was informative and the chapter on performance, tuning and maintenance was very useful.

This book would have been perfect a few years ago when I was setting up my current home file server which uses a pair of 40 GB drives in a software RAID-1 (mirroring) configuration. Since then, some of my partitions are now nearly full while others have plenty of free space. Rather than repartition, I've decided to build a replacement server with a RAID-5 configuration using three 120 GB drives.

While you can try and search the Internet for articles, I prefer reading from hard copy so I value books that do a good job of covering the material. This book came pretty darn close to addressing all of my questions except for one area.

At the time I ordered the book, a few people had mentioned "Linux Volume Management" which sounded very interesting. The copy I received was the first edition, dated December 2002, a time when LVM was itself relatively new. As such, there is no mention of LVM in this edition. Granted you'd almost need another book just to cover all of the details of LVM but since it is almost always used in concert with some kind of RAID, I felt the book should have had a section devoted to this important topic. Perhaps a chapter or two on this topic as well as a troubleshooting section could be added in a future edition.

The biggest difficulty with producing any book on Linux is that because it is constantly evolving, anything you write about can quickly become dated. I'd recommend this book as a good starting point for anyone interesting in learning about RAID on Linux especially if they come out with a 2nd edition with more info on LVM.

I've been in the RAID business (OEM) for about 6 years, this book has some errors, and bad logic. It may be OK if you are in it as a hobbyist. In the sample chapter he talks about setting up a 480 MB/sec SCSI 160 raid card for a web server. For that application, a simple hardware raid card, would work better, and have lower CPU overhead. On the higher end, where is the talk of fibre channel, drivers and stability? I'd skip this book - look for Designing Storage Area Networks: A Practical Reference for Implementing Fibre Channel SANs, Blueprints for High Availability: Designing Resilient Distributed Systems, and read on the net.

At the time of this review (2011) "Managing RAID on Linux" is a book that contains some very helpful information for RAID newbies but also contains much out-of-date material and perspectives. On the positive side, the book gives a good introductory overview of RAID, explaining: the fundamental issues involved (redundancy and performance); the various RAID levels and how they work; how software and hardware RAID fit into the overall Linux architecture; the basic mdadm procedures and commands; and other common issues and concerns. As promised by the title, a focus is maintained on the administrative aspects of RAID, such as planning, installation, configuration, and tuning.

Nevertheless much of the material, particularly on peripheral subjects, is outdated. The section for disk hardware focuses exclusively on SCSI and PATA technologies, with only a brief reference to SATA as an upcoming technology. At the time of writing, kernel 2.6 had not been released, and so discussions about patching and kernel options revolve around 2.0, 2.2, and 2.4. Mdadm (a software RAID management package) had just been released, so it is described and promoted in the book; however, a whole lot of material in the book is devoted to the raidtools package, which as far as I know is now defunct and obsolete. The chapter on hardware raid technologies is of course now many years out of date. The final section discussing file systems provides a perspective limited to 2002. The bulk of the discussion deals with ext2 versus ext3, along with a long promotion of reiserfs. XFS and JFS are also mentioned but only briefly, with no substantive technical discussion of their merits.

In brief, this is a well-written book and provides some useful introductory material. But if you can find a more recent, up-to-date treatise on the subject, you should buy that instead.