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 or SATA drives, then your first hard drive would be /dev/sda.

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 systems, these are called partitions.

Itanium systems use EFI, the Extensible Firmware Interface, for booting. The partition table format that EFI understands is called GPT, or GUID Partition Table. The partitioning program that understands GPT is called "parted", so that is the tool we will use below. Additionally, EFI can only read FAT filesystems, so that is the format to use for the EFI boot partition, where the kernel will be installed by "elilo".

The Installation CDs provide support for EVMS and LVM2. EVMS and LVM2 increase the flexibility offered by your partitioning setup. During the installation instructions, we will focus on "regular" partitions, but it is still good to know EVMS and LVM2 are supported as well.

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 parted 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:

• 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 and SATA.

As an example partitioning, we show you one for a 20GB disk, used as a demonstration laptop (containing webserver, mailserver, gnome, ...):

$ df -h
Filesystem    Type    Size  Used Avail Use% Mounted on
/dev/hda5     ext3    509M  132M  351M  28% /
/dev/hda2     ext3    5.0G  3.0G  1.8G  63% /home
/dev/hda7     ext3    7.9G  6.2G  1.3G  83% /usr
/dev/hda8     ext3   1011M  483M  477M  51% /opt
/dev/hda9     ext3    2.0G  607M  1.3G  32% /var
/dev/hda1     ext2     51M   17M   31M  36% /boot
/dev/hda6     swap    516M   12M  504M   2% <not mounted>
(Unpartitioned space for future usage: 2 GB)

/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.

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

Change your partition layout according to your own preference.

parted is the GNU partition editor. Fire up parted on your disk (in our example, we use /dev/sda):

# parted /dev/sda

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

GNU Parted 1.6.22
Copyright (C) 1998 - 2005 Free Software Foundation, Inc.
This program is free software, covered by the GNU General Public License.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without
even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
General Public License for more details.

Using /dev/sda
(parted)

At this point one of the available commands is help, which you should use if you want to see the other available commands. Another command is print which you should type next to display your disk's current partition configuration:

(parted) print
Disk geometry for /dev/sda: 0.000-34732.890 megabytes
Disk label type: gpt
Minor    Start       End     Filesystem  Name                  Flags
1          0.017    203.938  fat32                             boot
2        203.938   4243.468  linux-swap
3       4243.469  34724.281  ext3

This particular configuration is very similar to the one that we recommend above. Note on the second line that the partition table is type is GPT. If it is different, then the ia64 system will not be able to boot from this disk. For the sake of this guide we'll remove the partitions and create them anew.

The easy way to remove all partitions and start fresh, which guarantees that we are using the correct partition type, is to make a new partition table using the mklabel command. After you do this, you will have an empty GPT partition table.

(parted) mklabel gpt
(parted) print
Disk geometry for /dev/sda: 0.000-34732.890 megabytes
Disk label type: gpt
Minor    Start       End     Filesystem  Name                  Flags

Now that the 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 EFI boot partition. This is required to be a FAT filesystem in order for the ia64 firmware to read it. Our example makes this 32 megabytes, which is appropriate for storing kernels and elilo configuration. You can expect each ia64 kernel to be around 5 megabytes, so this configuration leaves you some room to grow and experiment.

(parted) mkpart primary fat32 0 32
(parted) print
Disk geometry for /dev/sda: 0.000-34732.890 megabytes
Disk label type: gpt
Minor    Start       End     Filesystem  Name                  Flags
1          0.017     32.000  fat32

Let's now create the swap partition. The classic size to make the swap partition was twice the amount of RAM in the system. In modern systems with lots of RAM, this is no longer necessary. For most desktop systems, a 512 megabyte swap partition is sufficient. For a server, you should consider something larger to reflect the anticipated needs of the server.

(parted) mkpart primary linux-swap 32 544
(parted) print
Disk geometry for /dev/sda: 0.000-34732.890 megabytes
Disk label type: gpt
Minor    Start       End     Filesystem  Name                  Flags
1          0.017     32.000  fat32
2         32.000    544.000

Finally, let's create the root partition. Our configuration will make the root partition to occupy the rest of the disk. We default to ext3, but you can use ext2, jfs, reiserfs or xfs if you prefer. The actual filesystem is not created in this step, but the partition table contains an indication of what kind of filesystem is stored on each partition, and it's a good idea to make the table match your intentions.

(parted) mkpart primary ext3 544 34732.890
(parted) print
Disk geometry for /dev/sda: 0.000-34732.890 megabytes
Disk label type: gpt
Minor    Start       End     Filesystem  Name                  Flags
1          0.017     32.000  fat32
2         32.000    544.000
3        544.000  34732.874

To quit from parted, type quit. There's no need to take a separate step to save your partition layout since parted has been saving it all along. As you leave, parted gives you reminder to update your /etc/fstab, which we'll do later in this guide.

(parted) quit
Information: Don't forget to update /etc/fstab, if necessary.

Now that your partitions are created, you can now 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.

vfat is the MS-DOS filesystem, updated to allow long filenames. It is also the only filesystem type that the EFI firmware on ia64 systems understand. The boot partition on ia64 systems should always be vfat, but for your data partitions you should use one of the other filesystems listed below.

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. It uses a hashed B*-tree index that enables high performance in almost all situations. In short, ext3 is a very good and reliable 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. ReiserFS is solid and usable as both general-purpose filesystem and for extreme cases such as the creation of large filesystems, very large files and directories containing tens of thousands of small files.

XFS is a filesystem with metadata journaling which 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 an 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 boot partition (/dev/sda1 in our example) as vfat and the root partition (/dev/sda3 in our example) as ext3, you would run the following commands:

# mkdosfs /dev/sda1
mkdosfs 2.10 (22 Sep 2003)

# mke2fs -j /dev/sda3
mke2fs 1.36 (05-Feb-2005)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
4382336 inodes, 8752348 blocks
437617 blocks (5.00%) reserved for the super user
First data block=0
268 block groups
32768 blocks per group, 32768 fragments per group
16352 inodes per group
Superblock backups stored on blocks: 
        32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208, 
        4096000, 7962624

Writing inode tables: done                            
Creating journal (8192 blocks): done
Writing superblocks and filesystem accounting information: done

This filesystem will be automatically checked every 26 mounts or
180 days, whichever comes first.  Use tune2fs -c or -i to override.

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

# mkswap /dev/sda2

To activate the swap partition, use swapon:

# swapon /dev/sda2

Create and activate the swap with the commands mentioned above.