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rane 05/09/20 18:48:24 |
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Added: xml/htdocs/doc/en/articles lvm-p1.xml lvm-p2.xml |
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Log: |
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two more articles, this time from #104169 |
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|
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Revision Changes Path |
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1.1 xml/htdocs/doc/en/articles/lvm-p1.xml |
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|
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file : http://www.gentoo.org/cgi-bin/viewcvs.cgi/xml/htdocs/doc/en/articles/lvm-p1.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/lvm-p1.xml?rev=1.1&content-type=text/plain&cvsroot=gentoo |
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|
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Index: lvm-p1.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/lvm-p1.xml,v 1.1 2005/09/20 18:48:24 rane Exp $ --> |
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|
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<guide link="/doc/en/articles/lvm-p1.xml"> |
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<title>Learning Linux LVM, Part 1</title> |
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|
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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: Joshua Saddler (jackdark@×××××.com) --> |
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|
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<abstract> |
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In this article, Daniel introduces you to the concepts behind Linux |
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LVM (Logical Volume Management) and shows you how to get the latest |
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kernel patches and tools installed on your system. LVM allows you to |
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create logical volumes out of the physical storage resources on your |
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machine. However, unlike physical volumes, the logical volumes can |
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be expanded and shrunk while the system is still running, providing |
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Linux system administrators with the storage flexibility that they've |
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until now only dreamed of. |
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</abstract> |
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|
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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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|
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<version>1.0</version> |
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<date>2005-08-29</date> |
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|
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<chapter> |
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<title>Storage management magic with Logical Volume Management</title> |
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<section> |
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<title>LVM intro</title> |
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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 |
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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 |
| 56 |
various improvements made by the Gentoo Linux Documentation team. |
| 57 |
</note> |
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|
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<p> |
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In this series, I'm going to show you how to install and use the new |
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Logical Volume Management support built-in to the Linux 2.4 kernel. If |
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you've never used a form of LVM before, you're in for a treat; it's a |
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wonderful technology. Before we actually get LVM up and running, I'm |
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going to explain exactly what it is and how it works. Then, we'll be |
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ready to test out LVM and get the most out of it. |
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</p> |
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|
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<p> |
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If you're like me, then your experience with UNIX and Linux began on |
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a PC platform, rather than on large, commercial UNIX servers and |
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workstations. On the basic PC, we've always had to deal with |
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partitioning our hard drives. PC people are generally well-acquainted |
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with tools such as <c>fdisk</c>, which are used to create and delete |
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primary and extended partitions on hard disks. Hard disk partitioning |
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is an annoying but accepted part of the process of getting an |
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operating system up and running. |
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</p> |
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|
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<p> |
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Hard drive partitioning can be annoying because to do a good job you |
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really need to accurately estimate how much space you'll need for |
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each partition. If you make a poor estimation, your Linux system |
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could possibly be crippled -- to fix the problem, it's possible that |
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you might even need to perform a full system backup, wipe your hard |
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drives clean, and then restore all your data to a new (and presumably |
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better) partition layout. Ick! These are exactly the kinds of |
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situations that sysadmins try their best to avoid in the first place. |
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</p> |
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|
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<p> |
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While partitions were once static storage regions, thankfully, we now |
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have a proliferation of PC repartitioning tools (PowerQuest's |
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Partition Magic product is one of the most popular). These tools allow |
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you to boot your system with a special disk and dynamically resize |
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your partitions and filesystems. Once you reboot, you have newly |
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resized partitions, hopefully getting you out of your storage crunch. |
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These partition resizing tools are great and solve the problem storage |
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management for some. But are they perfect? Not exactly. |
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</p> |
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|
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<p> |
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Tools like Partition Magic are great for workstations, but aren't |
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really adequate for servers. First of all, they require you to reboot |
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your system. This is something most sysadmins desperately try to avoid |
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doing. What if you simply can't reboot your machine every time your |
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storage needs change, such as if your storage needs change dramatically |
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on a weekly basis? What happens if you need to expand a filesystem so |
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that it spans more than one hard drive, or what do you do if you need |
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to dynamically expand or shrink a volume's storage capacity while |
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allowing Apache to continue to serve Web pages? In a highly available, |
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dynamic environment, a basic partition resizer just won't work. For |
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these and other situations, Logical Volume Management is an excellent |
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(if not perfect) solution. |
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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>Enter LVM</title> |
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<body> |
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|
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<p> |
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Now, let's take a look at how LVM solves these problems. To create an |
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LVM logical volume, we follow a three-step process. First, we need to |
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select the physical storage resources that are going to be used for |
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LVM. Typically, these are standard partitions but can also be Linux |
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software RAID volumes that we've created. In LVM terminology, these |
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storage resources are called "physical volumes". Our first step in |
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setting up LVM involves properly initializing these partitions so |
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that they can be recognized by the LVM system. This involves setting |
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the correct partition type if we're adding a physical partition, and |
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running the pvcreate command. |
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</p> |
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|
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<p> |
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Once we have one or more physical volumes initialized for use by LVM, |
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we can move on to step two -- creating a volume group. You can think |
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of a volume group as a pool of storage that consists of one or more |
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physical volumes. While LVM is running, we can add physical volumes |
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to the volume group or even remove them. However, we can't mount or |
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create filesystems on a volume group directly. Instead, we can tell |
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LVM to create one or more "logical volumes" using our volume group |
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storage pool: |
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</p> |
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|
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<figure link="/images/docs/l-lvm-1.gif" caption="A volume group is |
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created out of physical volumes"/> |
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|
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<p> |
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Creating an LVM logical volume is really easy, and once it's created |
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we can go ahead and put a filesystem on it, mount it, and start using |
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the volume to store our files. To create a logical volume, we use the |
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<c>lvcreate</c> command, specifying the name of our new volume, the |
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size we'd like the volume to be, and the volume group that we'd like |
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this particluar logical volume to be part of. The LVM system will |
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then allocate storage from the volume group we specify and create our |
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new volume, which is now ready for use. Once created, we can put an |
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ext2 or ReiserFS filesystem on it, mount it, and use it as we like. |
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</p> |
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|
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<figure link="/images/docs/l-lvm-2.gif" caption="Creating two |
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logical volumes from our existing volume group"/> |
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|
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</body> |
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</section> |
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<section> |
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<title>Extents</title> |
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<body> |
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|
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<p> |
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Behind the scenes, the LVM system allocates storage in equal-sized |
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"chunks", called extents. We can specify the particular extent size |
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to use at volume group creation time. The size of an extent defaults |
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to 4Mb, which is perfect for most uses. One of the beauties of LVM is |
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that the physical storage locations of the extents used for one of our |
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logical volumes (in other words, what disk they're stored on) can be |
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dynamically changed while our logical volume is mounted and in use! |
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The LVM system ensures that our logical volumes continue to operate |
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perfectly while allowing the administrator to physically change where |
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everything is stored. |
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</p> |
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|
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<p> |
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Of course, since everything is created out of equally-sized extents, |
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it's really easy to allocate some additional extents for an |
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already-existing logical volume -- in other words, dynamically "grow" |
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the volume: |
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</p> |
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|
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<figure link="/images/docs/l-lvm-3.gif" caption="Adding additional |
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extents from our volume group, expanding the size of our logical |
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volume"/> |
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|
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<p> |
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Once the logical volume has been expanded, you can then expand your |
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ext2 or ReiserFS filesystem to take advantage of this new space. If |
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you use a program such as <c>resize_reiserfs</c>, this filesystem |
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expansion can also happen while the volume is mounted and being used! |
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Truly amazing -- with LVM and online filesystem expansion utilties, |
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it's no longer necessary to reboot your system or even drop to |
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runlevel 1 to change your storage configuration. |
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</p> |
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|
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<p> |
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The only time you need to shut down your system is when you need to |
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add new physical disks. Once new disks have been added, you then can |
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add these new physical volumes to your volume group(s) to create a |
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fresh supply of extents. |
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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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|
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|
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|
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1.1 xml/htdocs/doc/en/articles/lvm-p2.xml |
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|
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file : http://www.gentoo.org/cgi-bin/viewcvs.cgi/xml/htdocs/doc/en/articles/lvm-p2.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/lvm-p2.xml?rev=1.1&content-type=text/plain&cvsroot=gentoo |
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|
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Index: lvm-p2.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/lvm-p2.xml,v 1.1 2005/09/20 18:48:24 rane Exp $ --> |
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|
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<guide link="/doc/en/articles/lvm-p2.xml"> |
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<title>Learning Linux LVM, Part 2</title> |
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|
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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: Joshua Saddler (jackdark@×××××.com) --> |
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|
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<abstract> |
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In this article, Daniel shares his experiences converting |
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cvs.gentoo.org's /home filesystem to an LVM logical volume. After |
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the transition, we get to see the benefits of LVM when |
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cvs.gentoo.org's /home partition is dynamically resized in real-time, |
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without rebooting, unmounting /home, or even dropping to runlevel 1. |
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All processes continue to work without any interruption. Daniel's |
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step-by-step details of the conversion will help anyone interested |
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in peforming a similiar transition on their own machine. |
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</abstract> |
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|
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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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|
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<version>1.0</version> |
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<date>2005-08-29</date> |
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|
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<chapter> |
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<title>The cvs.gentoo.org upgrade</title> |
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<section> |
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<title>Introduction</title> |
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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 |
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developerWorks, and is property of Westtech Information Services. This |
| 264 |
document is an updated version of the original article, and contains |
| 265 |
various improvements made by the Gentoo Linux Documentation team. |
| 266 |
</note> |
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|
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<p> |
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In <uri link="/doc/en/articles/lvm-p1.xml">my first LVM article</uri>, |
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I explained the concepts behind LVM. Now it's time to put LVM into |
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action. In this article, I'm going to set up LVM on the official Gentoo |
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Linux cvs server, cvs.gentoo.org. Although cvs.gentoo.org has only one |
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hard drive, LVM's flexibility still provides an incredible improvement |
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over the standard static partitioning approach. I'll show you all the |
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steps of the LVM conversion process, so that if you're interested you |
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can perform a similar conversion on one of your machines. |
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</p> |
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|
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<warn> |
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Because implementing LVM is a major change to the system (involving the |
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creation of new partitions and other potentially hazardous actions) |
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it's a really good idea to perform a full system backup before |
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beginning this process. If you're not going to perform a backup, I |
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hope you're using a test box with no important data on it. I should |
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mention that I didn't experience any problems while converting to LVM, |
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but it's best to be prepared in case something goes wrong. |
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</warn> |
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|
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<p> |
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That said, let's continue. Before starting the conversion process, I |
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upgraded cvs.gentoo.org so that it was using the following packages. At |
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the time I performed the LVM transition, these were the latest versions |
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available (see <uri link="#resources">Resources</uri> later in this |
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article): |
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</p> |
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|
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<ul> |
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<li>Linux kernel 2.4.1-ac19</li> |
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<li>LVM 0.9.1_beta5</li> |
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<li>reiserfs-utils 3.6.25</li> |
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</ul> |
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|
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<p> |
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Now, for the hard drive. cvs.gentoo.org had a nice new IBM 45 GB hard |
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drive sitting in it; however, when I installed Gentoo Linux on cvs, I |
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only partitioned about 10 gigabytes of the drive, keeping the remaining |
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35 GB for future partitions. Such are the little tricks you need to |
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employ when not using LVM -- leaving part of the drive unpartitioned is |
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a primitive but effective way to allow for future expansion. However, |
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with LVM there is a better approach. |
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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 space problem</title> |
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<body> |
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|
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<p> |
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In the past few weeks, I had been noticing that my root ReiserFS |
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partition had been slowly filling up, as you can see from this |
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<c>df</c> output: |
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</p> |
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|
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<pre caption="Shrinking free space"> |
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Filesystem 1k-blocks Used Available Use% Mounted on |
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/dev/hda3 9765200 6989312 2775888 72% / |
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tmpfs 269052 0 269052 0% /dev/shm |
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</pre> |
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|
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<p> |
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Now, a 72% full root partition isn't exactly a crisis, but it isn't a |
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wonderful situation either. ReiserFS, like many other filesystems, |
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starts slowing down as it gets more and more full, and it was just a |
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matter of time before my root filesystem would fill up completely and |
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filesystem performance would take a hit. |
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</p> |
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|
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<p> |
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I decided to fix this problem by using LVM to create a new logical |
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volume out of the 35 GB of currently unpartitioned space at the end |
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of my hard drive. Then, I'd create a filesystem on this volume and |
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move a good chunk of the contents of <path>/dev/hda3</path> to it. |
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</p> |
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|
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<p> |
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If you're thinking of making a similar transition on one of your |
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machines, the first thing you need to do is find a suitable piece of |
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your root filesystem to move to a logical volume. For me, the choice |
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was easy -- my <path>/home</path> tree was taking up around 5.7 GB. By |
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moving <path>/home</path> to its own LVM logical volume, my root |
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filesystem would then be at about 20% capacity. Since most new data is |
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being added to <path>/home</path>, my root filesystem would likely stay |
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at around 20% capacity as well -- a very healthy situation. |
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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 beginnings of a solution</title> |
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<body> |
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|
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<p> |
| 364 |
To begin the conversion, I first had to partition the unused space at |
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the end of my hard drive. Using <c>cfdisk</c>, I created a 35 GB |
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partition (<path>/dev/hda5</path>) and set the partition type of the |
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partition to <c>8E</c> (the official LVM partition type). After this |
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change, I rebooted to force a reread of my partition table. After the |
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reboot, my partition table looked like this: |
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</p> |
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|
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<pre caption="The new partition table"> |
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# <i>sfdisk -l</i> |
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Disk /dev/hda: 89355 cylinders, 16 heads, 63 sectors/track |
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Units = cylinders of 516096 bytes, blocks of 1024 bytes, counting from 0 |
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Device Boot Start End #cyls #blocks Id System |
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/dev/hda1 * 0+ 247 248- 124960+ 83 Linux |
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/dev/hda2 248 743 496 249984 82 Linux swap |
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/dev/hda3 744 20119 19376 9765504 83 Linux |
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/dev/hda4 20120 89354 69235 34894440 5 Extended |
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/dev/hda5 20120+ 89354 69235- 34894408+ 8e Linux LVM |
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</pre> |
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|
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<p> |
| 385 |
Now that I had an empty 35 GB partition, I was ready to initialize it |
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for LVM. Here's the procedure -- first, I would initialize the 35 |
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gigabytes as a <e>physical</e> volume; then, I would create a |
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<e>volume</e> group using this physical volume, and finally, I would |
| 389 |
allocate some of the extents on the volume group, creating a |
| 390 |
<e>logical volume</e> that would contain my new filesystem and house |
| 391 |
all the files currently in <path>/home</path>. |
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</p> |
| 393 |
|
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<p> |
| 395 |
To begin the process, I used the <c>pvcreate</c> command to |
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initialize <path>/dev/hda5</path> as a physical volume: |
| 397 |
</p> |
| 398 |
|
| 399 |
<pre caption="Creating the physical volume"> |
| 400 |
# <i>pvcreate /dev/hda5</i> |
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pvcreate -- physical volume "/dev/hda5" successfully created |
| 402 |
</pre> |
| 403 |
|
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<p> |
| 405 |
<c>pvcreate</c> set up a special "accounting" area on |
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<path>/dev/hda5</path>, called the VGDA (volume group descriptor |
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area). LVM uses this area to keep track of how the physical extents |
| 408 |
are allocated, among other things. |
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</p> |
| 410 |
|
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<p> |
| 412 |
My next step was to create a volume group and add |
| 413 |
<path>/dev/hda5</path> to this group. The volume group would act as a |
| 414 |
pool of extents (chunks of storage blocks). Once the volume group was |
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created, I could create as many logical volumes as I wanted. I decided |
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that my volume group would be called "main": |
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</p> |
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|
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<pre caption="Creating the volume group"> |
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# <i>vgcreate main /dev/hda5</i> |
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vgcreate -- INFO: using default physical extent size 4 MB |
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vgcreate -- INFO: maximum logical volume size is 255.99 Gigabyte |
| 423 |
|
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|
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|
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-- |
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