Introduction to block devices
Let's take a good look at disk-oriented aspects of Gentoo Linux and Linux in general, including block devices, partitions, and Linux filesystems. Once the ins and outs of disks are understood, partitions and filesystems can be established for installation.
To begin, let's look at block devices. SCSI and Serial ATA drives are both labeled under device handles such as: /dev/sda, /dev/sdb, /dev/sdc, etc. On more modern machines, PCI Express based NVMe solid state disks have device handles such as /dev/nvme0n1, /dev/nvme0n2, etc.
The following table will help readers determine where to find a certain type of block device on the system:
|Type of device||Default device handle||Editorial notes and considerations|
|IDE, SATA, SAS, SCSI, or USB flash||/dev/sda||Found on hardware from roughly 2007 until the present, this device handle is perhaps the most commonly used in Linux. These types of devices can be connected via the SATA bus, SCSI, USB bus as block storage. As example, the first partition on the first SATA device is called /dev/sda1.|
|NVM Express (NVMe)||/dev/nvme0n1||The latest in solid state technology, NVMe drives are connected to the PCI Express bus and have the fastest transfer block speeds on the market. Systems from around 2014 and newer may have support for NVMe hardware. The first partition on the first NVMe device is called /dev/nvme0n1p1.|
|MMC, eMMC, and SD||/dev/mmcblk0||embedded MMC devices, SD cards, and other types of memory cards can be useful for data storage. That said, many systems may not permit booting from these types of devices. It is suggested to not use these devices for active Linux installations; rather consider using them to transfer files, which is their typical design intention. Alternatively this storage type could be useful for short-term file backups or snapshots.|
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 4096-byte (4K) blocks.
Introduction to block devices
Placeholder for introduction to block devices specific to the relative architecture.
Designing a partition scheme
Placeholder for designing a partition scheme specific to the relative architecture.
Creating file systems
If using an SSD or NVMe drive, please check if it needs a firmware upgrade. Some Intel SSDs in particular (600p and 6000p) require a firmware upgrade for critical bug fixes avoid data corruption induced by XFS I/O usage patterns (though not through any fault of the filesystem). smartctl can help check the model and firmware version.
Now that the partitions have been 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...
Linux supports several dozen filesystems, although many of them are only wise to deploy for specific purposes. Only certain filesystems may be 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. XFS is the recommended all-purpose, all-platform filesystem. The below is a non-exhaustive list:
- Newer generation filesystem. Provides advanced features like 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. RAID 5/6 and quota groups unsafe on all versions of btrfs.
- Ext4 is a reliable, all-purpose all-platform filesystem, although it lacks modern features like reflinks.
- The Flash-Friendly File System was originally created by Samsung for the use with NAND flash memory. It is a decent choice when installing Gentoo to microSD cards, USB drives, or other flash-based storage devices.
- Filesystem with metadata journaling which comes with a robust feature-set and is optimized for scalability. It has been continuously upgraded to include modern features. The only downside is that XFS partitions cannot yet be shrunk, although this is being worked on. XFS notably supports reflinks and Copy on Write (CoW) which is particularly helpful on Gentoo systems because of the amount of compiles users complete. XFS is the recommended modern all-purpose all-platform filesystem. Requires a partition to be at least 300MB.
- Also known as FAT32, is supported by Linux but does not support standard UNIX permission settings. It is mostly used for interoperability/interchange with other operating systems (Microsoft Windows or Apple's macOS) but is also a necessity for some system bootloader firmware (like UEFI). Users of UEFI systems will need an EFI System Partition formatted with VFAT in order to boot.
- This "New Technology" filesystem is the flagship filesystem of Microsoft Windows since Windows NT 3.1. Similarly to VFAT, 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 for most cases. It should only be used for interoperability or data interchange with Microsoft Windows systems (note the emphasis on only).
More extensive information on filesystems can be found in the community maintained Filesystem article.
Applying a filesystem to a partition
Please make sure to emerge the relevant package for the chosen filesystem later on in the handbook, before rebooting at the end of the install process.
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|
For instance, to have the root partition () as as used in the example partition structure, the following commands would be used:
If using ext4 on a small partition (less than 8 GiB), then the file system must be created with the proper options to reserve enough inodes. This can be done using one of the following commands, respectively:
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.
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:
To activate the swap partition, use swapon:
Create and activate the swap with the commands mentioned above.
Mounting the root partition
Users of non-Gentoo installation media will need to create the mount point by running:
mkdir --parents /mnt/gentoo
Now that the partitions have been 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:
If /tmp/ needs to reside on a separate partition, be sure to change its permissions after mounting:
chmod 1777 /mnt/gentoo/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.