Btrfs/es

BTRFS es un sistema de archivos basado en el principio copy-on-write (COW) que fue inicialmente diseñado en Oracle Corporation para ser usado en Linux. El desarrollo de BTRFS comenzó en 2007 y desde agosto de 2014 este sistema ha sido marcado como estable.

En el año 2015, BTRFS fue adoptado como el sistema de archivos oficial de SUSE Linux Enterprise Server 12. SUSE ratificó su compromiso con BTRFS en 2017 después de que RedHat anunciara que dejaría de soportar este sistema de archivos.

BTRFS fue diseñado para mejorar algunas de las deficiencias de los sistemas de archivos en Linux, entre ellas: almacenamiento de archivos basado Extensión, espacio eficiente de almacenamiento de archivos pequeños, espacio eficiente directorios indexados, asignación dinámica de inodos, instantáneas de escritura --de sólo lectura instantáneas, subvolúmenes ( raíces del sistema de archivos interno separadas), sumas de verificación sobre los datos y metadatos (CRC32C), compresión (zlib y LZO) y soporte de múltiples dispositivos integrados.

It is easy to set up and use BTRFS. In this simple introduction, we're going to set up BTRFS under Funtoo Linux using an existing debian-sources or debian-sources-lts kernel, like the one that comes pre-built for you with Funtoo Linux, and we will also be using our BTRFS storage pool for storing data that isn't part of the Funtoo Linux installation itself. Funtoo Linux will boot from a non-BTRFS filesystem, and as part of the initialization process will initialize our BTRFS storage and mount it at the location of our choice.

Installation

To install BTRFS no aditional steps are needed as it is part of Linux Kernel (in mainline Linux kernel since 2.6.29). Let's emerge the BTRFS userspace tools (btrfs-progs):

root # emerge btrfs-progs

BTRFS is now ready for use.

BTRFS Concepts

BTRFS can be used to manage the physical disks that it uses, and physical disks are added to a BTRFS volume. Then, BTRFS can create subvolumes from the volume on which files can be stored.

Unlike traditional Linux filesystems, BTRFS filesystems will allocate storage on-demand from the underlying volume.

In the BTRFS world, the word volume corresponds to a storage pool (ZFS) or a volume group (LVM).

• devices - one or multiple underlying physical volumes.
• volume - one large storage pool comprised of all space of the devices and can support different redundancy levels
• subvolumes - these are what get mounted and you store files in.
• snapshots - a read-only copy of a subvolume at a given point in time and/or read-write copy of a subvolume in time (aka clone).

Creating a Volume

To create a basic BTRFS volume, you will need an extra empty disk. Perform the following steps:

root #  mkfs.btrfs /dev/sdxy
btrfs-progs v4.17.1 
See http://btrfs.wiki.kernel.org for more information.

Detected a SSD, turning off metadata duplication.  Mkfs with -m dup if you want to force metadata duplication.
Performing full device TRIM /dev/sdj (223.57GiB) ...
Label:              (null)
UUID:               d6bcba6e-8fd5-41fc-9bb4-79628c5c928c
Node size:          16384
Sector size:        4096
Filesystem size:    223.57GiB
Block group profiles:
  Data:             single            8.00MiB
  Metadata:         single            8.00MiB
  System:           single            4.00MiB
SSD detected:       yes
Incompat features:  extref, skinny-metadata
Number of devices:  1
Devices:
   ID        SIZE  PATH
    1   223.57GiB  /dev/sdxy

/dev/sdxy should be an unused disk. You may need to use the following command if this disk contains any pre-existing data on it:

root #  mkfs.btrfs -f /dev/sdxy

Now you can mount the created volume as you would mount any other linux filesystem.

root #  mkdir /data
root #  mount /dev/sdxy /data
root #  mount
...
/dev/sdxy on /data type btrfs (rw,relatime,ssd,space_cache,subvolid=5,subvol=/)

To automatically mount this volume after reboot you need to add a simple fstab entry:

/dev/sdxy	/data	btrfs	defaults	0 0

You should now be at the point where you can begin to use BTRFS for a variety of tasks. While there is a lot more to BTRFS than what is covered in this short introduction, you should now have a good understanding of the fundamental concepts on which BTRFS is based.