Johdatus levyosioihin

Tietojen tallentamiseksi levyasemaan on ensin alustettava levyasema. Alustaminen (tunnetaan yleensä nimellä "making a file system`") kirjoittaa tiedot asemaan ja luo järjestyksen alustamattoman aseman tyhjään tilaan.

Kuten Tiedostojärjestelmällä varustettu levyasema viittaa, tiedostojärjestelmän määräämään järjestykseen liittyy joitain kompromisseja:

Huomaa, että ei ole olemassa yhtä yleistä tiedostojärjestelmää. Kuten Levyasema eri tiedostojärjestelmällä osoittaa, levyasemaan voi olla kirjoitettu yksi monista eri tiedostojärjestelmistä. Eri tiedostojärjestelmät eivät yleensä ole yhteensopivia; toisin sanoen käyttöjärjestelmä, joka tukee yhtä tiedostojärjestelmää (tai kourallinen siihen liittyviä tiedostojärjestelmätyyppejä), ei välttämättä tue toista. Fedora tukee kuitenkin monenlaisia tiedostojärjestelmiä (mukaan lukien monet muiden käyttöjärjestelmien, kuten Microsoft Windowsin, yleisesti käyttämät tiedostot), mikä tekee tiedonsiirrosta eri tiedostojärjestelmien välillä helppoa.

Tiedostojärjestelmän kirjoittaminen levylle on vasta ensimmäinen askel. Tämän prosessin tavoitteena on itse asiassa tiedon tallennus ja haku. Alla oleva kuva näyttää levyaseman sen jälkeen, kun sille on kirjoitettu tietoja:

Kuten Levyasema, johon on kirjoitettu data osoittaa, jotkut aiemmin tyhjistä lohkoista sisältävät nyt tietoja. Pelkästään tätä kuvaa katsomalla emme kuitenkaan voi määrittää tarkalleen, kuinka monta tiedostoa tällä asemalla on. Tiedostoja voi olla vain yksi tai useita, koska kaikki tiedostot käyttävät vähintään yhtä lohkoa ja jotkut tiedostot käyttävät useita lohkoja. Toinen tärkeä huomioitava seikka on, että käytettyjen lohkojen ei tarvitse muodostaa yhtenäistä aluetta; Käytettyjä ja käyttämättömiä lohkoja voi olla välissä. Tämä tunnetaan nimellä fragmentation. Sirpaloituminen voi vaikuttaa, kun yritetään muuttaa olemassa olevan osion kokoa.

Kuten useimmat tietokoneisiin liittyvät tekniikat, levyasemat muuttuivat ajan myötä niiden käyttöönoton jälkeen. Erityisesti ne kasvoivat. Ei suurempia fyysisesti, mutta suurempia niiden talletuskapasiteetissa. Ja tämä lisäkapasiteetti muutti perustavanlaatuisesti levyasemien käyttöä.

Disk drives can be divided into partitions. Each partition can be accessed as if it was a separate disk. This is done through the addition of a partition table.

There are several reasons for allocating disk space into separate disk partitions, for example:

There are currently two partitioning layout standards for physical hard disks: Master Boot Record (MBR) and GUID Partition Table (GPT). MBR is an older method of disk partitioning used with BIOS-based computers. GPT is a newer partitioning layout that is a part of the Unified Extensible Firmware Interface (UEFI). This section and Partitions Within Partitions - An Overview of Extended Partitions mainly describe the Master Boot Record (MBR) disk partitioning scheme. For information about the GUID Partition Table (GPT) partitioning layout, see GUID Partition Table (GPT).

As Disk Drive with Partition Table shows, the partition table is divided into four sections or four primary partitions. A primary partition is a partition on a hard drive that can contain only one logical drive (or section). Each section can hold the information necessary to define a single partition, meaning that the partition table can define no more than four partitions.

Each partition table entry contains several important characteristics of the partition:

The starting and ending points define the partition’s size and location on the disk. The “active” flag is used by some operating systems’ boot loaders. In other words, the operating system in the partition that is marked “active” is booted.

The type is a number that identifies the partition’s anticipated usage. Some operating systems use the partition type to denote a specific file system type, to flag the partition as being associated with a particular operating system, to indicate that the partition contains a bootable operating system, or some combination of the three.

See Disk Drive With Single Partition for an example of a disk drive with single partition.

The single partition in this example is labeled as DOS. This label shows the partition type, with DOS being one of the most common ones. The table below shows a list of some of the commonly used partition types and hexadecimal numbers used to represent them.

In case four partitions are insufficient for your needs, you can use extended partitions to create up additional partitions. You do this by setting the type of a partition to “Extended”.

An extended partition is like a disk drive in its own right - it has its own partition table which points to one or more partitions (now called logical partitions, as opposed to the four primary partitions) contained entirely within the extended partition itself. Disk Drive With Extended Partition, shows a disk drive with one primary partition and one extended partition containing two logical partitions (along with some unpartitioned free space).

As this figure implies, there is a difference between primary and logical partitions - there can only be four primary partitions, but there is no fixed limit to the number of logical partitions that can exist. However, due to the way in which partitions are accessed in Linux, no more than 12 logical partitions should be defined on a single disk drive.

GUID Partition Table (GPT) is a newer partitioning scheme based on using Globally Unique Identifiers (GUID). GPT was developed to cope with limitations of the MBR partition table, especially with the limited maximum addressable storage space of a disk. Unlike MBR, which is unable to address storage space larger than 2.2 terabytes, GPT can be used with hard disks larger than this; the maximum addressable disk size is 2.2 zettabytes. In addition, GPT by default supports creating up to 128 primary partitions. This number could be extended by allocating more space to the partition table.

GPT disks use logical block addressing (LBA) and the partition layout is as follows:

In this situation, the partitions already defined do not span the entire hard disk, leaving unallocated space that is not part of any defined partition. Disk Drive with Unpartitioned Free Space, shows what this might look like.

In the above example, 1 represents an undefined partition with unallocated space and 2 represents a defined partition with allocated space.

An unused hard disk also falls into this category. The only difference is that all the space is not part of any defined partition.

In any case, you can create the necessary partitions from the unused space. Unfortunately, this scenario, although very simple, is not very likely (unless you have just purchased a new disk just for Fedora). Most pre-installed operating systems are configured to take up all available space on a disk drive (see Using Free Space from an Active Partition).

In this case, maybe you have one or more partitions that you do not use any longer. Disk Drive with an Unused Partition, illustrates such a situation.

In the above example, 1 represents an unused partition and 2 represents reallocating an unused partition for Linux.

In this situation, you can use the space allocated to the unused partition. You first must delete the partition and then create the appropriate Linux partition(s) in its place. You can delete the unused partition and manually create new partitions during the installation process.

This is the most common situation. It is also, unfortunately, the hardest to handle. The main problem is that, even if you have enough free space, it is presently allocated to a partition that is already in use. If you purchased a computer with pre-installed software, the hard disk most likely has one massive partition holding the operating system and data.

Aside from adding a new hard drive to your system, you have two choices:

Each step is described further in more detail.

Linux uses a naming scheme that is file-based, with file names in the form of /dev/xxyN.

Device and partition names consist of the following:

Each partition is used to form part of the storage necessary to support a single set of files and directories. This is done by associating a partition with a directory through a process known as mounting. Mounting a partition makes its storage available starting at the specified directory (known as a mount point).

For example, if partition /dev/sda5 is mounted on /usr/, that would mean that all files and directories under /usr/ physically reside on /dev/sda5. So the file /usr/share/doc/FAQ/txt/Linux-FAQ would be stored on /dev/sda5, while the file /etc/gdm/custom.conf would not.

Continuing the example, it is also possible that one or more directories below /usr/ would be mount points for other partitions. For instance, a partition (say, /dev/sda7) could be mounted on /usr/local/, meaning that /usr/local/man/whatis would then reside on /dev/sda7 rather than /dev/sda5.

At this point in the process of preparing to install Fedora, you should give some consideration to the number and size of the partitions to be used by your new operating system. However, there is no one right answer to this question. It depends on your needs and requirements.

Unless you have a reason for doing otherwise, you should at least create a /boot partition and a / (root) partition. Depending on your system’s hardware specifications, additional partitions may be necessary, such as /boot/efi for 64-bit AMD, Intel and Arm systems with UEFI firmware, a biosboot partition for AMD and Intel systems with a GUID Partition Table (GPT) label on the system disk, or a PReP Boot partition on IBM Power Systems servers.

See Recommended Partitioning Scheme for more information about the recommended partitioning scheme.