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[ << ] [ < ] [ Home ] [ > ] [ >> ] 4. Preparing the DisksContent:
4.a. 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. These are called partitions. 4.b. Designing a Partitioning Scheme 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 disadvantages as well. If not configured properly, you will have a system with lots of free space on one partition and none on another. Another nuisance is that separate partitions - especially for important mountpoints like /usr or /var - often require the administrator to boot with an initramfs to mount the partition before other boot scripts start. This isn't always the case though, so your results may vary. There is also a 15-partition limit for SCSI and SATA. 4.c. Using fdisk on MIPS to Partition your Disk SGI Machines: Creating an SGI Disk Label All disks in an SGI System require an SGI Disk Label, which serves a similar function as Sun & MS-DOS disklabels -- It stores information about the disk partitions. Creating a new SGI Disk Label will create two special partitions on the disk:
The following is an example excerpt from an fdisk session. Read and tailor it to your needs...
Getting the SGI Volume Header to just the right size
Now that an SGI Disklabel is created, partitions may now be defined. In the above example, there are already two partitions defined for you. These are the special partitions mentioned above and should not normally be altered. However, for installing Gentoo, we'll need to load a bootloader, and possibly multiple kernel images (depending on system type) directly into the volume header. The volume header itself can hold up to eight images of any size, with each image allowed eight-character names. The process of making the volume header larger isn't exactly straight-forward; there's a bit of a trick to it. One cannot simply delete and re-add the volume header due to odd fdisk behavior. In the example provided below, we'll create a 50MB Volume header in conjunction with a 50MB /boot partition. The actual layout of your disk may vary, but this is for illustrative purposes only.
If you're unsure how to use fdisk have a look down further at the instructions for partitioning on Cobalts. The concepts are exactly the same -- just remember to leave the volume header and whole disk partitions alone. Once this is done, you are safe to create the rest of your partitions as you see fit. After all your partitions are laid out, make sure you set the partition ID of your swap partition to 82, which is Linux Swap. By default, it will be 83, Linux Native. Now that your partitions are created, you can continue with Creating Filesystems. Cobalt Machines: Partitioning your drive On Cobalt machines, the BOOTROM expects to see a MS-DOS MBR, so partitioning the drive is relatively straightforward -- in fact, it's done the same way as you'd do for an Intel x86 machine. However there are some things you need to bear in mind.
For that reason, I recommend creating a ~20MB /boot partition formatted EXT2r0 upon which you can install CoLo & your kernels. This allows you to run a modern filesystem (EXT3 or ReiserFS) for your root filesystem. I will assume you have created /dev/sda1 to mount later as a /boot partition. If you wish to make this /, you'll need to keep the PROM's expectations in mind. So, continuing on... To create the partitions you type fdisk /dev/sda at the prompt. The main commands you need to know are these:
And that's all there is to it. You should now be right to proceed onto the next stage: 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... Several filesystems are available. ReiserFS, EXT2, EXT3 and EXT4 are found stable on the MIPS architectures, others are experimental. 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. The mke2fs application uses the "bytes-per-inode" setting to calculate how many inodes a file system should have. By running mke2fs -T small /dev/<device> the number of inodes will generally quadruple for a given file system as its "bytes-per-inode" reduces from one every 16kB to one every 4kB. You can tune this even further by using mke2fs -i <ratio> /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. 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. The mke2fs application uses the "bytes-per-inode" setting to calculate how many inodes a file system should have. By running mke2fs -j -T small /dev/<device> the number of inodes will generally quadruple for a given file system as its "bytes-per-inode" reduces from one every 16kB to one every 4kB. You can tune this even further by using mke2fs -j -i <ratio> /dev/<device>. ext4 is a filesystem created as a fork of ext3 bringing new features, performance improvements and removal of size limits with moderate changes to the on-disk format. It can span volumes up to 1 EB and with maximum file size of 16 TB. Instead of the classic ext2/3 bitmap block allocation ext4 uses extents, which improve large file performance and reduce fragmentation. Ext4 also provides more sophisticated block allocation algorithms (delayed allocation and multiblock allocation) giving the filesystem driver more ways to optimise the layout of data on the disk. The ext4 filesystem is a compromise between production-grade code stability and the desire to introduce extensions to an almost decade old filesystem. Ext4 is the recommended all-purpose all-platform filesystem. 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 ext4, you would use:
Now create the filesystems on your newly created partitions (or logical volumes).
mkswap is the command that is used to create and 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. [ << ] [ < ] [ Home ] [ > ] [ >> ] The contents of this document, unless otherwise expressly stated, are licensed under the CC-BY-SA-2.5 license. The Gentoo Name and Logo Usage Guidelines apply. |
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