|
1. Introduction to Block Devices We'll take a good look at disk-oriented aspects of Gentoo Linux and Linux in general, including Linux filesystems, partitions and block devices. Then, once you're familiar with the ins and outs of disks and filesystems, you'll be guided through the process of setting up partitions and filesystems for your Gentoo Linux installation. To begin, we'll introduce block devices. The most famous block device is probably the one that represents the first drive in a Linux system, namely /dev/sda. SCSI and Serial ATA drives are both labeled /dev/sd*; even IDE drives are labeled /dev/sd* with the new libata framework in the kernel. If you're using the old device framework, then your first IDE drive is /dev/hda. The block devices above represent an abstract interface to the disk. User programs can use these block devices to interact with your disk without worrying about whether your drives are IDE, SCSI or something else. The program can simply address the storage on the disk as a bunch of contiguous, randomly-accessible 512-byte blocks. Although it is theoretically possible to use a full disk to house your Linux system, this is almost never done in practice. Instead, full disk block devices are split up in smaller, more manageable block devices. On ${arch} systems, these are called partitions. Partitions are divided in three types: primary, extended and logical. A primary partition is a partition which has its information stored in the MBR (master boot record). As an MBR is very small (512 bytes) only four primary partitions can be defined (for instance, /dev/sda1 to /dev/sda4). An extended partition is a special primary partition (meaning the extended partition must be one of the four possible primary partitions) which contains more partitions. Such a partition didn't exist originally, but as four partitions were too few, it was brought to life to extend the formatting scheme without losing backward compatibility. A logical partition is a partition inside the extended partition. Their definitions aren't placed inside the MBR, but are declared inside the extended partition. 1. Designing a Partitioning Scheme
If you are not interested in drawing up a partitioning scheme for your system, you can use the partitioning scheme we use throughout this book:
If you are interested in knowing how big a partition should be, or even how many partitions you need, read on. Otherwise continue now with partitioning your disk by reading Using fdisk to Partition your Disk. The number of partitions is highly dependent on your environment. For instance, if you have lots of users, you will most likely want to have your /home separate as it increases security and makes backups easier. If you are installing Gentoo to perform as a mailserver, your /var should be separate as all mails are stored inside /var. A good choice of filesystem will then maximise your performance. Gameservers will have a separate /opt as most gaming servers are installed there. The reason is similar for /home: security and backups. You will definitely want to keep /usr big: not only will it contain the majority of applications, the Portage tree alone takes around 500 Mbyte excluding the various sources that are stored in it. As you can see, it very much depends on what you want to achieve. Separate partitions or volumes have the following advantages:
However, multiple partitions have one big disadvantage: if not configured properly, you might result in having a system with lots of free space on one partition and none on another. There is also a 15-partition limit for SCSI and SATA. As an example partitioning, we show you one for a 20GB disk, used as a demonstration laptop (containing webserver, mailserver, gnome, ...):
/usr is rather full (83% used) here, but once all software is installed, /usr doesn't tend to grow that much. Although allocating a few gigabytes of disk space for /var may seem excessive, remember that Portage uses this partition by default for compiling packages. If you want to keep /var at a more reasonable size, such as 1GB, you will need to alter your PORTAGE_TMPDIR variable in /etc/make.conf to point to the partition with enough free space for compiling extremely large packages such as OpenOffice. 1. Using fdisk to Partition your Disk The following parts explain how to create the example partition layout described previously, namely:
Change your partition layout according to your own preference. Viewing the Current Partition Layout fdisk is a popular and powerful tool to split your disk into partitions. Fire up fdisk on your disk (in our example, we use /dev/sda):
Once in fdisk, you'll be greeted with a prompt that looks like this:
Type p to display your disk's current partition configuration:
This particular disk is configured to house seven Linux filesystems (each with a corresponding partition listed as "Linux") as well as a swap partition (listed as "Linux swap"). We will first remove all existing partitions from the disk. Type d to delete a partition. For instance, to delete an existing /dev/sda1:
The partition has been scheduled for deletion. It will no longer show up if you type p, but it will not be erased until your changes have been saved. If you made a mistake and want to abort without saving your changes, type q immediately and hit enter and your partition will not be deleted. Now, assuming that you do indeed want to wipe out all the partitions on your system, repeatedly type p to print out a partition listing and then type d and the number of the partition to delete it. Eventually, you'll end up with a partition table with nothing in it:
Now that the in-memory partition table is empty, we're ready to create the partitions. We will use a default partitioning scheme as discussed previously. Of course, don't follow these instructions to the letter if you don't want the same partitioning scheme! We first create a small boot partition. Type n to create a new partition, then p to select a primary partition, followed by 1 to select the first primary partition. When prompted for the first cylinder, hit enter. When prompted for the last cylinder, type +32M to create a partition 32 Mbyte in size:
Now, when you type p, you should see the following partition printout:
We need to make this partition bootable. Type a to toggle the bootable flag on a partition and select 1. If you press p again, you will notice that an * is placed in the "Boot" column. Let's now create the swap partition. To do this, type n to create a new partition, then p to tell fdisk that you want a primary partition. Then type 2 to create the second primary partition, /dev/sda2 in our case. When prompted for the first cylinder, hit enter. When prompted for the last cylinder, type +512M to create a partition 512MB in size. After you've done this, type t to set the partition type, 2 to select the partition you just created and then type in 82 to set the partition type to "Linux Swap". After completing these steps, typing p should display a partition table that looks similar to this:
Finally, let's create the root partition. To do this, type n to create a new partition, then p to tell fdisk that you want a primary partition. Then type 3 to create the third primary partition, /dev/sda3 in our case. When prompted for the first cylinder, hit enter. When prompted for the last cylinder, hit enter to create a partition that takes up the rest of the remaining space on your disk. After completing these steps, typing p should display a partition table that looks similar to this:
To save the partition layout and exit fdisk, type w.
Now that your partitions are created, you can continue with Creating Filesystems. Now that your partitions are created, it is time to place a filesystem on them. If you don't care about what filesystem to choose and are happy with what we use as default in this handbook, continue with Applying a Filesystem to a Partition. Otherwise read on to learn about the available filesystems... The Linux kernel supports various filesystems. We'll explain ext2, ext3, ReiserFS, XFS and JFS as these are the most commonly used filesystems on Linux systems. ext2 is the tried and true Linux filesystem but doesn't have metadata journaling, which means that routine ext2 filesystem checks at startup time can be quite time-consuming. There is now quite a selection of newer-generation journaled filesystems that can be checked for consistency very quickly and are thus generally preferred over their non-journaled counterparts. Journaled filesystems prevent long delays when you boot your system and your filesystem happens to be in an inconsistent state. If you intend to install Gentoo on a very small disk (less than 4GB), then you'll need to tell ext2 to reserve enough inodes when you create the filesystem by running mke2fs -T small /dev/<device>. ext3 is the journaled version of the ext2 filesystem, providing metadata journaling for fast recovery in addition to other enhanced journaling modes like full data and ordered data journaling. It uses an HTree index that enables high performance in almost all situations. In short, ext3 is a very good and reliable filesystem. Ext3 is the recommended all-purpose all-platform filesystem. If you intend to install Gentoo on a very small disk (less than 4GB), then you'll need to tell ext3 to reserve enough inodes when you create the filesystem by running mke2fs -j -T small /dev/<device>. JFS is IBM's high-performance journaling filesystem. JFS is a light, fast and reliable B+tree-based filesystem with good performance in various conditions. ReiserFS is a B+tree-based journaled filesystem that has good overall performance, especially when dealing with many tiny files at the cost of more CPU cycles. ReiserFS appears to be less maintained than other filesystems. XFS is a filesystem with metadata journaling which comes with a robust feature-set and is optimized for scalability. XFS seems to be less forgiving to various hardware problems. Applying a Filesystem to a Partition To create a filesystem on a partition or volume, there are tools available for each possible filesystem:
For instance, to have the boot partition (/dev/sda1 in our example) in ext2 and the root partition (/dev/sda3 in our example) in ext3 (as in our example), you would use:
Now create the filesystems on your newly created partitions (or logical volumes). mkswap is the command that is used to initialize swap partitions:
To activate the swap partition, use swapon:
Create and activate the swap with the commands mentioned above. Now that your partitions are initialized and are housing a filesystem, it is time to mount those partitions. Use the mount command. Don't forget to create the necessary mount directories for every partition you created. As an example we mount the root and boot partition:
We will also have to mount the proc filesystem (a virtual interface with the kernel) on /proc. But first we will need to place our files on the partitions. Continue with (Installing the Gentoo Installation Files). |
|
