rane 05/10/01 17:16:24 Added: xml/htdocs/doc/en/articles l-afig-p8.xml Log: new article from #103294
Revision Changes Path 1.1 xml/htdocs/doc/en/articles/l-afig-p8.xml file : http://www.gentoo.org/cgi-bin/viewcvs.cgi/xml/htdocs/doc/en/articles/l-afig-p8.xml?rev=1.1&content-type=text/x-cvsweb-markup&cvsroot=gentoo plain: http://www.gentoo.org/cgi-bin/viewcvs.cgi/xml/htdocs/doc/en/articles/l-afig-p8.xml?rev=1.1&content-type=text/plain&cvsroot=gentoo Index: l-afig-p8.xml =================================================================== <?xml version='1.0' encoding='UTF-8'?> <!DOCTYPE guide SYSTEM "/dtd/guide.dtd"> <!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/articles/l-afig-p8.xml,v 1.1 2005/10/01 17:16:24 rane Exp $ --> <guide link="/doc/en/articles/l-afig-p8.xml"> <title>Advanced filesystem implementor's guide, Part 8</title> <author title="Author"> <mail link="[EMAIL PROTECTED]">Daniel Robbins</mail> </author> <!-- xmlified by David H. Askew ([EMAIL PROTECTED])--> <!-- The original version of this article was first published on IBM developerWorks, and is property of Westtech Information Services. This document is an updated version of the original article, and contains various improvements made by the Gentoo Linux Documentation team --> <abstract> With the 2.4 release of Linux come many new filesystem possibilities, including Reiserfs, XFS, GFS, and others. These filesystems sound cool, but what exactly can they do, what are they good at, and exactly how do you go about safely using them in a production Linux environment? Daniel Robbins answers these questions by showing you how to set up these new advanced filesystems under Linux 2.4. In this installment, Daniel continues his look at ext3, a new improved version of ext2 with journaling capabilities. He reveals all the inside information on ext3, and demonstrates some shockingly good ext3 data=journal interactive performance numbers. </abstract> <version>1.0</version> <date>2005-09-30</date> <chapter> <title>Introduction</title> <section> <body> <note> The original version of this article was first published on IBM developerWorks, and is property of Westtech Information Services. This document is an updated version of the original article, and contains various improvements made by the Gentoo Linux Documentation team. </note> <p> I'm going to be honest. For this article, I was planning to show you how to get ext3 up and running on your system. Although that's what I said I'd do, I'm not going to do it. Andrew Morton's excellent "Using the ext3 filesystem in 2.4 kernels" page (see <uri link="#resources">Resources</uri> later in this article) already does a great job of explaining how to ext3-enable your system, so there's no need for me to repeat all the basics here. Instead, I'm going to delve into some meatier ext3 topics, ones that I think you'll find very useful. After you read this article, when you're ready to get ext3 up and running, head over to Andrew's page. </p> </body> </section> </chapter> <chapter> <title>2.4 kernel update</title> <section> <body> <p> First, let's start with a 2.4 kernel update. I last discussed 2.4 kernel stability when I was covering ReiserFS. Way back then, finding a stable 2.4 kernel was a challenge, and I recommended sticking with the known and at that time bleeding-edge 2.4.4-ac9 kernel -- especially for anyone planning to use the ReiserFS filesystem in a production environment. As you might guess, a lot has happened since 2.4.4-ac9, and it's definitely time to start looking at newer kernels. </p> <p> With kernel 2.4.10, the 2.4 series reached a new level of performance and scalability (something that we've been anticipating for a long time). So, what happened to allow Linux 2.4 to finally grow up? In an acronym, VM. Linus, recognizing that the 2.4 series wasn't performing spectacularly, ripped out Linux's problematic VM code and replaced it with a lean and mean VM implementation from Andrea Archangeli. Andrea's new VM implementation (which first appeared in 2.4.10) was really great; it really sped up the kernel and made the entire system more responsive. 2.4.10 was definitely a major turning point in 2.4 Linux kernel development; up until then, things weren't looking very good, and many of us were wondering why we weren't FreeBSD developers. We all should thank Linus for his heroism in making such a major (but sorely needed) change in the 2.4 stable kernel series. </p> <p> Since Andrea's new VM code needed a bit of time to be integrated seamlessly with the rest of the kernel, use 2.4.13+. Even better, use 2.4.16+, since the rock-solid ext3 filesystem code was finally integrated into the official Linus kernel starting with the 2.4.15-pre2 release. There's no reason to avoid using 2.4.16+ kernel, and it'll make your job of getting ext3 up and running that much easier. If you do use a 2.4.16+ kernel, just remember that it's no longer necessary to apply the ext3 patch as described on Andrew's page (see <uri link="#resources">Resources</uri>). Linus already added it for you. :) </p> <p> You'll notice that I recommend using 2.4.16+ rather than 2.4.15+, and with good reason. With the release of kernel 2.4.15-pre9, a really ugly filesystem corruption bug was introduced to the kernel. It took until 2.4.16-pre1 for the problem to be identified and fixed, resulting in a span of kernels (including 2.4.15) that should be avoided at all costs. Choosing a 2.4.16+ kernel allows you to avoid this bad batch entirely. </p> </body> </section> </chapter> <chapter> <title>Laptops...beware?</title> <section> <body> <p> Ext3 has a stellar reputation for being a rock-solid filesystem, so I was surprised to learn that quite a few laptop users were having filesystem corruption problems when they switched to ext3. In general, it's tempting to react to these kinds of reports by avoiding ext3 entirely; however, after asking around, I discovered that the disk corruption problems that people were experiencing had nothing to do with ext3 itself, but were being caused by certain laptop hard drives. </p> </body> </section> <section> <title>The write cache</title> <body> <p> You may not know this, but most modern hard drives have something called a "write cache", used by the hard drive to collect pending write operations. By putting pending writes into a cache, the hard drive firmware can then reorder and group them so that they're written to disk in the fastest possible way. The write cache is generally considered to be a very good thing (read Linus' explanation and opinion of write caching in <uri link="#resources">Resources</uri>). </p> <p> Unfortunately, certain laptop hard drives now on the market have the dubious feature of ignoring any official ATA request to flush their write cache to disk. This isn't a wonderful design feature, although it has been allowed by the ATA spec up until recently. With these types of drives, there's no way for the kernel to guarantee that a particular block has actually been recorded to the disk platters. Although this sounds like a thorny problem, this particular issue by itself is probably not the cause of the data corruption problems that people have been experiencing. </p> <p> However, it gets worse. Some modern laptop hard drives have an even nastier habit of throwing away their write cache whenever the system is rebooted or suspended. Obviously, if a hard drive has both of these problems, it's going to regularly corrupt data, and there's nothing that Linux can do to prevent it from doing so. </p> <p> So, what's the solution? If you have a laptop, tread carefully. Back up all your important files before making any major change to your filesystems. If you experience data corruption problems that seem to fit the pattern of what I described above, particularly with ext3, then remember that it may be your laptop hard drive that's at fault. In that case, you may want to contact your laptop manufacturer and inquire about getting a replacement drive. Hopefully, in a few months time, these flaky hard drives will be pulled from the market and we'll never need to worry about this issue again. </p> <p> Now that I've scared you out of your minds, let's take a look at ext3's various data journaling options. </p> </body> </section> </chapter> <chapter> <title>Journaling options and write latency</title> <section> <body> <p> Ext3 allows you to choose from one of three data journaling modes at filesystem mount time: data=writeback, data=ordered, and data=journal. </p> <p> To specify a journal mode, you can add the appropriate string (data=journal, for example) to the options section of your /etc/fstab, or specify the -o data=journal command-line option when calling mount directly. If you'd like to -- [email protected] mailing list
