Status

From btrfs Wiki
Revision as of 09:36, 22 September 2016 by Hans van Kranenburg (Talk | contribs)

Jump to: navigation, search

Contents

Overview

For a list of features by their introduction, please see the table Changelog#By_feature.

The following table aims to give an overview of the stability of the features BTRFS supports in the latest kernel version (4.7). This refers to functionality, not usability (as this would need to specify the usecase and expectations).

Feature Status Notes
Subvolumes, snapshots OK
Trim (aka. discard) OK fstrim and mounted with -o discard (has performance implications)
Autodefrag OK
Defrag mostly OK extents get unshared (see below)
Auto-repair OK automatically repair from a correct spare copy if possible (dup, raid1, raid10)
Compression mostly OK (needs verification and source) auto-repair and compression may crash
Scrub OK
Scrub + RAID56 Unstable will verify but not repair
Filesystem resize OK shrink, grow
Send OK corner cases may still exist
Receive OK
Single (block group profile) OK
DUP (block group profile) OK
RAID0 OK
RAID1 OK
RAID10 OK
RAID56 Unstable write hole still exists, parity not checksummed
Seeding OK should be better documented
Device replace mostly OK gets stuck on devices with bad sectors
Balance OK
Quotas, qgroups mostly OK
Out-of-band dedupe mostly OK performance issues
File range cloning mostly OK (reflink), heavily referenced extents have a noticeable performance hit
Offline UUID change OK
Free space tree Unstable see below
no-holes OK see documentation for compatibility
skinny-metadata OK see documentation for compatibility
extended-refs OK see documentation for compatibility
Mixed block groups OK see documentation
nodatacow OK (see below)

Legend:

  • OK: should be safe to use, no known defficiencies
  • mostly OK: safe for general use, there are some known problems
  • Unstable: do not use for other then testing purposes, known severe problems, missing implementation of some core part

Note to editors: please update the table if:

  • you're sure you know the answer, eg. a bug number for a bug that lowers the feature status
  • a particular feature combination that has a different status and is worth mentioning separately
  • there's a missing entry (put TBD to the status)
  • a reference could be enhanced by an actual link to documentation (wiki, manual pages)

The page edits are watched by wiki admins, do not worry to edit.

Details that do not fit the table

Defrag

The data affected by the defragmentation process will be newly written and will consume new space, the links to the original extents will not be kept. See also Manpage/btrfs-filesystem. Though autodefrag affects newly written data, it can read a few adjacent blocks (up to 64k) and write the contiguous extent to a new location. The adjacent blocks will be unshared. This happens on a smaller scale than the on-demand defrag and doesn't have the same impact.

Nodatacow

Nodatacow does not checksum data, see Manpage/btrfs(5).

Free space tree

Other

On-disk format

The filesystem disk format is stable. This means it is not expected to change unless there are very strong reasons to do so. If there is a format change, filesystems which implement the previous disk format will continue to be mountable and usable by newer kernels.

The core of the on-disk format that comprises building blocks of the filesystem:

  • layout of the main data structures, eg. superblock, b-tree nodes, b-tree keys, block headers
  • the COW mechanism, based on the original design of Ohad Rodeh's paper "Shadowing and clones"

Newly introduced features build on top of the above and could add specific structures. If a backward compatibility is not possible to maintain, a bit in the filesystem superblock denotes that and the level of incompatibility (full, read-only mount possible).

Personal tools