Handbook:Parts/Installation/Disks

Parts Handbook
Installation
About the installation
Choosing the media
Configuring the network
Preparing the disks
The stage file
Installing base system
Configuring the kernel
Configuring the system
Installing tools
Configuring the bootloader
Finalizing
Working with Gentoo
Portage introduction
USE flags
Portage features
Initscript system
Environment variables
Working with Portage
Files and directories
Variables
Mixing software branches
Additional tools
Custom package repository
Advanced features
OpenRC network configuration
Getting started
Advanced configuration
Modular networking
Wireless
Adding functionality
Dynamic management

Introduction to block devices

Block devices

Let's take a good look at disk-oriented aspects of Gentoo Linux and Linux in general, including Linux filesystems, partitions, and block devices. Once the ins and outs of disks and filesystems are understood, partitions and filesystems can be established for the Gentoo Linux installation.

To begin, let's look at 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*. On modern machines you may encounter block devices as, e.g., /dev/nvme0n1; these are PCI-Express based NVMe solid state disks.

The block devices above represent an abstract interface to the disk. User programs can use these block devices to interact with the disk without worrying about whether the drives are SATA, SCSI, or something else. The program can simply address the storage on the disk as a bunch of contiguous, randomly-accessible 512-byte blocks.

Introduction to block devices

Block devices

Note
Placeholder for introduction to block devices specific to the relative architecture.

Designing a partition scheme

Note
Placeholder for designing a partition scheme specific to the relative architecture.

Creating file systems

Introduction

Now that the partitions are created, it is time to place a filesystem on them. In the next section the various file systems that Linux supports are described. Readers that already know which filesystem to use can continue with Applying a filesystem to a partition. The others should read on to learn about the available filesystems...

Filesystems

Several filesystems are available. Some of them are found stable on the amd64 architecture - it is advised to read up on the filesystems and their support state before selecting a more experimental one for important partitions.

btrfs

A next generation filesystem that provides many advanced features such as snapshotting, self-healing through checksums, transparent compression, subvolumes, and integrated RAID. Kernels prior to 5.4.y are not guaranteed to be safe to use with btrfs in production because fixes for serious issues are only present in the more recent releases of the LTS kernel branches. Filesystem corruption issues are common on older kernel branches, with anything older than 4.4.y being especially unsafe and prone to corruption. Corruption is more likely on older kernels (than 5.4.y) when compression is enabled. RAID 5/6 and quota groups unsafe on all versions of btrfs. Furthermore, btrfs can counter-intuitively fail filesystem operations with ENOSPC when df reports free space due to internal fragmentation (free space pinned by DATA + SYSTEM chunks, but needed in METADATA chunks). Additionally, a single 4K reference to a 128M extent inside btrfs can cause free space to be present, but unavailable for allocations. This can also cause btrfs to return ENOSPC when free space is reported by df. Installing sys-fs/btrfsmaintenance and configuring the scripts to run periodically can help to reduce the possibility of ENOSPC issues by rebalancing btrfs, but it will not eliminate the risk of ENOSPC when free space is present. Some workloads will never hit ENOSPC while others will. If the risk of ENOSPC in production is unacceptable, you should use something else. If using btrfs, be certain to avoid configurations known to have issues. With the exception of ENOSPC, information on the issues present in btrfs in the latest kernel branches is available at the btrfs wiki status page.

ext2

This 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 the system is booted and the filesystem happens to be in an inconsistent state.

ext3

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.

ext4

Initially created as a fork of ext3, ext4 brings 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 16TB. 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 optimize the layout of data on the disk. Ext4 is the recommended all-purpose all-platform filesystem.

f2fs

The Flash-Friendly File System was originally created by Samsung for the use with NAND flash memory. As of Q2, 2016, this filesystem is still considered immature, but it is a decent choice when installing Gentoo to microSD cards, USB drives, or other flash-based storage devices.

JFS

IBM's high-performance journaling filesystem. JFS is a light, fast and reliable B+tree-based filesystem with good performance in various conditions.

ReiserFS

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 is not included in the mainline Linux kernel, and therefore is not recommended to be used when initially installing Gentoo.

XFS

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, but has been continuously upgraded to include modern features.

VFAT

Also known as FAT32, is supported by Linux but does not support standard UNIX permission settings. It is mostly used for interoperability with other operating systems (Microsoft Windows or Apple's OSX) but is also a necessity for some system bootloader firmware (like UEFI).

NTFS

This "New Technology" filesystem is the flagship filesystem of Microsoft Windows since Windows NT 3.1. Similar to vfat above it does not store UNIX permission settings or extended attributes necessary for BSD or Linux to function properly, therefore it should not be used as a root filesystem. It should only be used for interoperability with Microsoft Windows systems (note the emphasis on only).

When using ext2, ext3, or ext4 on a small partition (less than 8GB), then the file system must be created with the proper options to reserve enough inodes. The mke2fs (mkfs.ext2) application uses the "bytes-per-inode" setting to calculate the number of inodes for a file system. On smaller partitions, it is advised to increase the calculated number of inodes.

On ext2, ext3 and ext4, this can be done using one of the following commands, respectively:

root #mkfs.ext2 -T small /dev/<device>

root #mkfs.ext3 -T small /dev/<device>

root #mkfs.ext4 -T small /dev/<device>

This will generally quadruple the number of inodes for a given file system as its "bytes-per-inode" reduces from one every 16kB to one every 4kB. This can be tuned even further by providing the ratio:

root #mkfs.ext2 -i <ratio> /dev/<device>

Applying a filesystem to a partition

To create a filesystem on a partition or volume, there are user space utilities available for each possible filesystem. Click the filesystem's name in the table below for additional information on each filesystem:

Filesystem	Creation command	On minimal CD?	Package
btrfs	mkfs.btrfs	Yes	sys-fs/btrfs-progs
ext2	mkfs.ext2	Yes	sys-fs/e2fsprogs
ext3	mkfs.ext3	Yes	sys-fs/e2fsprogs
ext4	mkfs.ext4	Yes	sys-fs/e2fsprogs
f2fs	mkfs.f2fs	Yes	sys-fs/f2fs-tools
jfs	mkfs.jfs	Yes	sys-fs/jfsutils
reiserfs	mkfs.reiserfs	Yes	sys-fs/reiserfsprogs
xfs	mkfs.xfs	Yes	sys-fs/xfsprogs
vfat	mkfs.vfat	Yes	sys-fs/dosfstools
NTFS	mkfs.ntfs	Yes	sys-fs/ntfs3g

For instance, to have the boot partition (/dev/sda1) in ext2 and the root partition (/dev/sda3) in ext4 as used in the example partition structure, the following commands would be used:

root #mkfs.ext2 /dev/sda1

root #mkfs.ext4 /dev/sda3

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

Activating the swap partition

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

root #mkswap /dev/sda2

To activate the swap partition, use swapon:

root #swapon /dev/sda2

Create and activate the swap with the commands mentioned above.

Mounting the root partition

Now that the partitions are initialized and are housing a filesystem, it is time to mount those partitions. Use the mount command, but don't forget to create the necessary mount directories for every partition created. As an example we mount the root partition:

root #mount /dev/sda3 /mnt/gentoo

Note
If /tmp/ needs to reside on a separate partition, be sure to change its permissions after mounting:

root #chmod 1777 /mnt/gentoo/tmp

This also holds for /var/tmp.

Later in the instructions the proc filesystem (a virtual interface with the kernel) as well as other kernel pseudo-filesystems will be mounted. But first we install the Gentoo installation files.

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