|
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 Alpha systems, these are called slices. 1. Designing a Partitioning Scheme As an example we use the following slice layout:
If you are interested in knowing how big a partition should be, or even how many partitions (or volumes) you need, read on. Otherwise continue now with Using fdisk to Partition your Disk (SRM only) or Using fdisk to Partition your Disk (ARC/AlphaBIOS only). 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 YMMV. 1. Using fdisk to Partition your Disk (SRM only) The following parts explain how to create the example slice layout described previously, namely:
Change your slice layout according to your own preference. To figure out what disks you have running, use the following commands:
From this output you should be able to see what disks were detected and their respective /dev entry. In the following parts we assume that the disk is a SCSI disk on /dev/sda. Now fire up fdisk:
If your hard drive is completely blank, then you'll have to first create a BSD disklabel.
We start with deleting all slices except the 'c'-slice (a requirement for using BSD disklabels). The following shows how to delete a slice (in the example we use 'a'). Repeat the process to delete all other slices (again, except the 'c'-slice). Use p to view all existing slices. d is used to delete a slice.
After repeating this process for all slices, a listing should show you something similar to this:
On Alpha based systems you don't need a separate boot slice. However, the first cylinder cannot be used as the aboot image will be placed there. We will create a swap slice starting at the third cylinder, with a total size of 1 GB. Use n to create a new slice. After creating the slice, we will change its type to 1 (one), meaning swap.
After these steps you should see a layout similar to the following:
We will now create the root slice, starting from the first cylinder after the swap slice. Use the p command to view where the swap slice ends. In our example, this is at 1003, making the root slice start at 1004. Another problem is that there is currently a bug in fdisk making it think the number of available cylinders is one above the real number of cylinders. In other words, when you are asked for the last cylinder, decrease the cylinder number (in this example: 5290) with one. When the slice is created, we change the type to 8, for ext2.
Your slice layout should now be similar to this:
Save the Slice Layout and Exit Save fdisk by typing w. This will also save your slice layout.
Now that your slices are created, you can continue with Creating Filesystems. 1. Using fdisk to Partition your Disk (ARC/AlphaBIOS only) The following parts explain how to partition the disk with a layout similar to the one described previously, namely:
Change your partition layout according to your own preference. To figure out what disks you have running, use the following commands:
From this output you should be able to see what disks were detected and their respective /dev entry. In the following parts we assume that the disk is a SCSI disk on /dev/sda. Now fire up fdisk:
If your hard drive is completely blank, then you'll have to first create a DOS disklabel.
We start with deleting all partitions. The following shows how to delete a partition (in the example we use '1'). Repeat the process to delete all other partitions. Use p to view all existing partitions. d is used to delete a partition.
On Alpha systems which use MILO to boot, we have to create a small vfat boot partition.
We will create a swap partition with a total size of 1 GB. Use n to create a new partition.
After these steps you should see a layout similar to the following:
We will now create the root partition. Again, just use the n command.
After these steps you should see a layout similar to the following:
Save the Partition Layout and Exit Save fdisk by typing w. This will also save your partition layout.
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, ext4, 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>. 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. 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 root partition (/dev/sda2 in our example) in ext3, 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 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). |
|