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