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 IDE drive in a Linux system, namely /dev/hda. If your system uses SCSI drives, then your first hard drive would be /dev/sda. Serial ATA drives are also /dev/sda even if they are IDE drives.

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 most systems, these are called partitions. Other architectures use a similar technique, called slices.

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 Apple G5: Using mac-fdisk to Partition your Disk or IBM pSeries: 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.

As you can see, it very much depends on what you want to achieve. Separate partitions or volumes have the following advantages:

• You can choose the best performing filesystem for each partition or volume
• Your entire system cannot run out of free space if one defunct tool is continuously writing files to a partition or volume
• If necessary, file system checks are reduced in time, as multiple checks can be done in parallel (although this advantage is more with multiple disks than it is with multiple partitions)
• Security can be enhanced by mounting some partitions or volumes read-only, nosuid (setuid bits are ignored), noexec (executable bits are ignored) etc.

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.

The following parts explain how to create the example partition layout described previously, namely:

Change your partition layout according to your own will.

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):

# fdisk /dev/sda

Once in fdisk, you'll be greeted with a prompt that looks like this:

Command (m for help):

Type p to display your disk's current partition configuration:

Command (m for help): p

Disk /dev/sda: 30.7 GB, 30750031872 bytes
141 heads, 63 sectors/track, 6761 cylinders
Units = cylinders of 8883 * 512 = 4548096 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/hdb1               1          12       53266+  83  Linux
/dev/hdb2              13         233      981571+  82  Linux swap
/dev/hdb3             234         674     1958701+  83  Linux
/dev/hdb4             675        6761    27035410+   5  Extended
/dev/hdb5             675        2874     9771268+  83  Linux
/dev/hdb6            2875        2919      199836   83  Linux
/dev/hdb7            2920        3008      395262   83  Linux
/dev/hdb8            3009        6761    16668918   83  Linux

Command (m for help):

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:

Command (m for help): d
Partition number (1-4): 1

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:

Disk /dev/sda: 30.7 GB, 30750031872 bytes
141 heads, 63 sectors/track, 6761 cylinders
Units = cylinders of 8883 * 512 = 4548096 bytes

Device Boot    Start       End    Blocks   Id  System

Command (m for help):

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 PReP 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 +7M to create a partition 7 Mbyte in size. After you've done this, type t to set the partition type, 1 to select the partition you just created and then type in 41 to set the partition type to "PPC PReP Boot".

Command (m for help): p

Disk /dev/sda: 30.7 GB, 30750031872 bytes
141 heads, 63 sectors/track, 6761 cylinders
Units = cylinders of 8883 * 512 = 4548096 bytes

   Device Boot      Start         End      Blocks   Id  System

Command (m for help): n
Command action
      e   extended
      p   primary partition (1-4)
p
Partition number (1-4): 1
First cylinder (1-6761, default 1): 
Using default value 1
Last cylinder or +size or +sizeM or +sizeK (1-6761, default
6761): +8M

Command (m for help): t
Selected partition 1
Hex code (type L to list codes): 41
Changed system type of partition 1 to 41 (PPC PReP Boot)

Command (m for help):

Now, when you type p, you should see the following partition printout:

Command (m for help): p

Disk /dev/sda: 30.7 GB, 30750031872 bytes
141 heads, 63 sectors/track, 6761 cylinders
Units = cylinders of 8883 * 512 = 4548096 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/hdb1               1           3       13293   41  PPC PReP Boot

Command (m for help):

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:

Command (m for help): p

Disk /dev/sda: 30.7 GB, 30750031872 bytes
141 heads, 63 sectors/track, 6761 cylinders
Units = cylinders of 8883 * 512 = 4548096 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/hdb1               1           3       13293   41  PPC PReP Boot
/dev/hdb2               4         117      506331   82  Linux swap

Command (m for help):

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:

Command (m for help): p

Disk /dev/sda: 30.7 GB, 30750031872 bytes
141 heads, 63 sectors/track, 6761 cylinders
Units = cylinders of 8883 * 512 = 4548096 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/hdb1               1           3       13293   41  PPC PReP Boot
/dev/hdb2               4         117      506331   82  Linux swap
/dev/hdb3             118        6761    29509326   83  Linux

Command (m for help):

To save the partition layout and exit fdisk, type w.

Command (m for help): w

Now that your partitions are created, you can now continue with Creating Filesystems.

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.

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. ext3 is a very good and reliable filesystem. It has an additional hashed b-tree indexing option that enables high performance in almost all situations. In short, ext3 is an excellent filesystem.

ReiserFS is a B*-tree based filesystem that has very good overall performance and greatly outperforms both ext2 and ext3 when dealing with small files (files less than 4k), often by a factor of 10x-15x. ReiserFS also scales extremely well and has metadata journaling. As of kernel 2.4.18+, ReiserFS is solid and usable as both general-purpose filesystem and for extreme cases such as the creation of large filesystems, the use of many small files, very large files and directories containing tens of thousands of files.

XFS is a filesystem with metadata journaling that is fully supported under Gentoo Linux's xfs-sources kernel. It comes with a robust feature-set and is optimized for scalability. We only recommend using this filesystem on Linux systems with high-end SCSI and/or fibre channel storage and a uninterruptible power supply. Because XFS aggressively caches in-transit data in RAM, improperly designed programs (those that don't take proper precautions when writing files to disk and there are quite a few of them) can lose a good deal of data if the system goes down unexpectedly.

JFS is IBM's high-performance journaling filesystem. It has recently become production-ready and there hasn't been a sufficient track record to comment positively nor negatively on its general stability at this point.

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/sda4 in our example) in ext3 (as in our example), you would use:

# mke2fs -j /dev/sda4

Now create the filesystems on your newly created partitions (or logical volumes).

mkswap is the command that is used to initialize swap partitions:

# mkswap /dev/sda3

To activate the swap partition, use swapon:

# swapon /dev/sda3

Create and activate the swap now.