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Difference between revisions of "Btrfs"
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= | =Btrfs is a modern CoW file system= | ||
A modern '''C'''opy '''o'''n '''W'''rite file system for Linux aimed at implementing advanced features while also focusing on '''fault tolerance''', '''repair''' and '''easy administration'''. Btrfs not only is a file system, but also is partly a volume manager, software-raid, backup-tool, and it is flash-friendly. | A modern '''C'''opy '''o'''n '''W'''rite file system for Linux aimed at implementing advanced features while also focusing on '''fault tolerance''', '''repair''' and '''easy administration'''. Btrfs not only is a file system, but also is partly a volume manager, software-raid, backup-tool, and it is flash-friendly. | ||
Because | Because Btrfs is different, some things seem unfamiliar and strange. Then [https://btrfs.wiki.kernel.org/index.php/Main_Page btrfs.wiki.kernel.org] is a good starting point to search for answers. | ||
Development of Btrfs started in 2007. Since that time, Btrfs is a part of the Linux kernel and is under active development. The Btrfs code base is '''[https://btrfs.wiki.kernel.org/index.php/Status stable] .''' However, new features are still under development. Its main features and benefits are: | Development of Btrfs started in 2007. Since that time, Btrfs is a part of the Linux kernel and is under active development. The Btrfs code base is '''[https://btrfs.wiki.kernel.org/index.php/Status stable] .''' However, new features are still under development. Its main features and benefits are: | ||
*'''Snapshots''' which do not make the full copy of files | *'''Snapshots''' which do not make the full copy of files | ||
*'''RAID''' - support for software-based RAID 0, RAID 1, RAID 10 | *'''RAID''' - support for software-based RAID 0, RAID 1, RAID 10 | ||
*'''Self-healing''' - checksums for data and metadata, automatic detection of silent data | *'''Self-healing''' - checksums for data and metadata, automatic detection of silent data corruption (see [https://btrfs.wiki.kernel.org/index.php/Main_Page btrfs@kernel.org], [https://wiki.archlinux.org/title/Btrfs Btrfs@ARC-wiki], [https://de.wikipedia.org/wiki/Btrfs Btrfs@wikipedia]) | ||
=== Familiar with btrfs-slang ? === | === Familiar with btrfs-slang ? === | ||
Because Btrfs is different, you will find some words that do have a special meaning when used for btrfs. This may be a source of confusion. | Because Btrfs is different, you will find some words that do have a special meaning when used for btrfs. This may be a source of confusion. | ||
<div class="mw-collapsible mw-collapsed"><div class="mw-collapsible-toggle" style="float:none;">▶ Btrfs '''volume'''</div><div class="mw-collapsible-content">A '''volume''' is a pool of raw storage and consists of one or more '''device'''s. The size of the volume will be the addition of all devices that are part of this volume. In most cases you will only use one Btrfs volume. You are able to add/remove devices at any time. ''Usually you do '''not''' mount a | <div class="mw-collapsible mw-collapsed"><div class="mw-collapsible-toggle" style="float:none;">▶ Btrfs '''volume'''</div><div class="mw-collapsible-content">A '''volume''' is a pool of raw storage and consists of one or more '''device'''s. The size of the volume will be the addition of all devices that are part of this volume. In most cases you will only use one Btrfs volume. You are able to add/remove devices at any time. ''Usually you do '''not''' mount a Btrfs volume.'' | ||
</div></div> | </div></div> | ||
<div class="mw-collapsible mw-collapsed"><div class="mw-collapsible-toggle" style="float:none;">▶ Btrfs '''chunk'''</div><div class="mw-collapsible-content">A '''chunk''' is simply a piece of storage that Btrfs can use to put data on. Think of a chunk(usually 1GiB) as of a page in a book. The book is the volume, and the chunk is one page of it. When you start, all pages are empty. When you write data to the volume, one page(chunk) after the other is written to. | <div class="mw-collapsible mw-collapsed"><div class="mw-collapsible-toggle" style="float:none;">▶ Btrfs '''chunk'''</div><div class="mw-collapsible-content">A '''chunk''' is simply a piece of storage that Btrfs can use to put data on. Think of a chunk(usually 1GiB) as of a page in a book. The book is the volume, and the chunk is one page of it. When you start, all pages are empty. When you write data to the volume, one page (="chunk") after the other is written to. | ||
</div></div> | </div></div> | ||
<div class="mw-collapsible mw-collapsed"><div class="mw-collapsible-toggle" style="float:none;">▶ '''device'''</div><div class="mw-collapsible-content">A '''device''' is some linux device. It may be '''a partition''' like '''/dev/sdz1''' or /dev/sdz2. Or it may be a raw disk device like /dev/sdz without any partitioning. A Btrfs volume consists of '''at least one device'''. | <div class="mw-collapsible mw-collapsed"><div class="mw-collapsible-toggle" style="float:none;">▶ '''device'''</div><div class="mw-collapsible-content">A '''device''' is some linux device. It may be '''a partition''' like '''/dev/sdz1''' or /dev/sdz2. Or it may be a raw disk device like /dev/sdz without any partitioning. A Btrfs volume consists of '''at least one device'''. | ||
</div></div> | </div></div> | ||
<div class="mw-collapsible mw-collapsed"><div class="mw-collapsible-toggle" style="float:none;">▶ Btrfs '''subvolume'''</div><div class="mw-collapsible-content">A Btrfs subvolume is an independently mountable POSIX | <div class="mw-collapsible mw-collapsed"><div class="mw-collapsible-toggle" style="float:none;">▶ Btrfs '''subvolume'''</div><div class="mw-collapsible-content">A Btrfs subvolume is an independently mountable POSIX file-tree and '''not a block device'''. It is the part of a volume that will be '''mounted writeable''' into your Linux system. By convention the names of subvolumes start with @ ('''@''', '''@home''', '''@snapshots''' ...). All subvolumes share the space of the Btrfs volume. You may create subvolumes at will. (You may think of subvolumes ''as sort of "dynamic partitions" inside a Btrfs volume'') | ||
</div></div> | </div></div> | ||
<div class="mw-collapsible mw-collapsed"><div class="mw-collapsible-toggle" style="float:none;">▶ '''default subvolume''' </div><div class="mw-collapsible-content">The default subvolume of a Btrfs volume is special. When you mount, you normally have to name a subvolume to mount. When you don't name a subvolume, the default subvolume will be used by mount. The default subvolume can be changed to any subvolume. It is advisable to set that subvolume as default, that is used for mounting linux '''"/"''' this is often the subvolume with name '''"@"''' | <div class="mw-collapsible mw-collapsed"><div class="mw-collapsible-toggle" style="float:none;">▶ '''default subvolume''' </div><div class="mw-collapsible-content">The default subvolume of a Btrfs volume is special. When you mount, you normally have to name a subvolume to mount. When you don't name a subvolume, the default subvolume will be used by mount. The default subvolume can be changed to any subvolume. It is advisable to set that subvolume as default, that is used for mounting linux '''"/"''' this is often the subvolume with name '''"@"''' | ||
</div></div> | </div></div> | ||
<div class="mw-collapsible mw-collapsed"><div class="mw-collapsible-toggle" style="float:none;">▶ Btrfs '''volume-root''' "/", Btrfs '''layout''' </div><div class="mw-collapsible-content">A Btrfs volume contains one ore more subvolumes. But they are not stored in form of a list. These subvolumes are stored in a tree-like structure like in a filesystem. Sometimes called the "top-level subvolume" or "root of the volume". But be | <div class="mw-collapsible mw-collapsed"><div class="mw-collapsible-toggle" style="float:none;">▶ Btrfs '''volume-root''' "/", Btrfs '''layout''' </div><div class="mw-collapsible-content">A Btrfs volume contains one ore more subvolumes. But they are not stored in form of a list. These subvolumes are stored in a tree-like structure like in a filesystem. Sometimes called the "top-level subvolume" or "root of the volume". But be careful this is '''not linux-root "/"''', but Btrfs '''volume-root "/"'''. There are several basic schemas to '''layout''' subvolumes in a volume | ||
</div></div> | </div></div> | ||
<div class="mw-collapsible mw-collapsed"><div class="mw-collapsible-toggle" style="float:none;">▶ Btrfs '''snapshot'''</div><div class="mw-collapsible-content">A snapshot looks nearly the same as a subvolume. But don´t get confused. When we talk about snapshots we usually mean a "''' | <div class="mw-collapsible mw-collapsed"><div class="mw-collapsible-toggle" style="float:none;">▶ Btrfs '''snapshot'''</div><div class="mw-collapsible-content">A snapshot looks nearly the same as a subvolume. But don´t get confused. When we talk about snapshots we usually mean a "'''Read-Only (RO) photograph''' of a subvolume". While the subvolume changes with time. A snapshot stays in the state of the subvolume at the time we made it. You can mount snapshots into your linux system, but you only can read the content. And the content will never change while this snapshot exists. When creating '''snapshots''' you have to watch out for the Btrfs-'''layout''' in use. | ||
It is possible to make a | It is possible to make a writeable subvolume out of a RO snapshot. This is the way roll back does work. | ||
</div></div> | </div></div> | ||