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178 lines
4.7 KiB
Plaintext
178 lines
4.7 KiB
Plaintext
[[chapter_btrfs]]
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BTRFS
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-----
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ifdef::wiki[]
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:pve-toplevel:
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endif::wiki[]
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BTRFS is a modern copy on write file system natively supported by the Linux
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kernel, implementing features such as snapshots, built-in RAID and self healing
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via checksums for data and metadata. Starting with {pve} 7.0, BTRFS is
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introduced as optional selection for the root file system.
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.General BTRFS advantages
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* Main system setup almost identical to the traditional ext4 based setup
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* Snapshots
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* Data compression on file system level
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* Copy-on-write clone
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* RAID0, RAID1 and RAID10
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* Protection against data corruption
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* Self healing
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* natively supported by the Linux kernel
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* ...
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.Caveats
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* RAID levels 5/6 are experimental and dangerous
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Installation as Root File System
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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When you install using the {pve} installer, you can choose BTRFS for the root
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file system. You need to select the RAID type at installation time:
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[horizontal]
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RAID0:: Also called ``striping''. The capacity of such volume is the sum
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of the capacities of all disks. But RAID0 does not add any redundancy,
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so the failure of a single drive makes the volume unusable.
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RAID1:: Also called ``mirroring''. Data is written identically to all
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disks. This mode requires at least 2 disks with the same size. The
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resulting capacity is that of a single disk.
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RAID10:: A combination of RAID0 and RAID1. Requires at least 4 disks.
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The installer automatically partitions the disks and creates an additional
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subvolume at `/var/lib/pve/local-btrfs`. In order to use that with the {pve}
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tools, the installer creates the following configuration entry in
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`/etc/pve/storage.cfg`:
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----
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dir: local
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path /var/lib/vz
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content iso,vztmpl,backup
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disable
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btrfs: local-btrfs
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path /var/lib/pve/local-btrfs
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content iso,vztmpl,backup,images,rootdir
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----
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This explicitly disables the default `local` storage in favor of a btrfs
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specific storage entry on the additional subvolume.
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The `btrfs` command is used to configure and manage the btrfs file system,
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After the installation, the following command lists all additional subvolumes:
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----
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# btrfs subvolume list /
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ID 256 gen 6 top level 5 path var/lib/pve/local-btrfs
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----
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BTRFS Administration
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~~~~~~~~~~~~~~~~~~~~
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This section gives you some usage examples for common tasks.
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Creating a BTRFS file system
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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To create BTRFS file systems, `mkfs.btrfs` is used. The `-d` and `-m` parameters
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are used to set the profile for metadata and data respectively. With the
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optional `-L` parameter, a label can be set.
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Generally, the following modes are supported: `single`, `raid0`, `raid1`,
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`raid10`.
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Create a BTRFS file system on `/dev/sdb1`
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----
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# mkfs.btrfs -m single -d single -L My-Storage /dev/sdb1
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----
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Or create a RAID1 on `/dev/sdb1` and `/dev/sdc1`
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----
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# mkfs.btrfs -m raid1 -d raid1 -L My-Storage /dev/sdb1 /dev/sdc1
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----
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This can then be mounted or used in `/etc/fstab` like any other mount point.
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For example
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----
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# mkdir /my-storage
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# mount /dev/sdb1 /my-storage
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----
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Creating a subvolume
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^^^^^^^^^^^^^^^^^^^^
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Creating a subvolume links it to a path in the btrfs file system, where it will
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appear as a regular directory.
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----
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# btrfs subvolume create /some/path
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----
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Afterwards `/some/path` will act like a regular directory.
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Deleting a subvolume
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^^^^^^^^^^^^^^^^^^^^
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Contrary to directories removed via `rmdir`, subvolumes do not need to be empty
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in order to be deleted via the `btrfs` command.
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----
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# btrfs subvolume delete /some/path
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----
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Creating a snapshot of a subvolume
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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BTRFS does not actually distinguish between snapshots and normal subvolumes, so
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taking a snapshot can also be seen as creating an arbitrary copy of a subvolume.
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By convention, {pve} will use the read-only flag when creating snapshots of
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guest disks or subvolumes, but this flag can also be changed later on.
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----
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# btrfs subvolume snapshot -r /some/path /a/new/path
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----
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This will create a read-only "clone" of the subvolume on `/some/path` at
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`/a/new/path`. Any future modifications to `/some/path` cause the modified data
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to be copied before modification.
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If the read-only (`-r`) option is left out, both subvolumes will be writable.
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Enabling compression
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^^^^^^^^^^^^^^^^^^^^
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By default, BTRFS does not compress data. To enable compression, the `compress`
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mount option can be added. Note that data already written will not be compressed
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after the fact.
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By default, the rootfs will be listed in `/etc/fstab` as follows:
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----
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UUID=<uuid of your root file system> / btrfs defaults 0 1
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----
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You can simply append `compress=zstd`, `compress=lzo`, or `compress=zlib` to the
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`defaults` above like so:
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----
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UUID=<uuid of your root file system> / btrfs defaults,compress=zstd 0 1
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----
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This change will take effect after rebooting.
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