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btrfs-space-calculator - calculate usable and wasted space


btrfs-space-calculator [args] sizes


The btrfs-space-calculator program shows the amount of allocatable space on btrfs physical and virtual level, and the amount of unallocatable space resulting from having differently sized block devices added to the filesystem.

In a btrfs filesystem, raw storage is shared by data of different types (System, MetaData and Data) and profiles (e.g. single, DUP, RAID1). Also, a filesystem can have multiple block devices of different sizes attached.

An example:

-$ btrfs-space-calculator -m raid1 -d raid1 2TB 500G 1TB
Target metadata profile: RAID1
Target data profile: RAID1
Mixed block groups: False
Total raw filesystem size: 3.18TiB
Device sizes:
Device 1: 1.82TiB
Device 2: 465.66GiB
Device 3: 931.32GiB
Metadata to data ratio: 1:200
Estimated virtual space to use for metadata: 7.00GiB
Estimated virtual space to use for data: 1.36TiB
Total unallocatable raw amount: 465.66GiB
Unallocatable raw bytes per device:
Device 1: 465.66GiB
Device 2: 0.00B
Device 3: 0.00B

Note that most physical disk vendors specify their sizes in GB or TB for deceptive marketing reasons, while partitions created in your average partition table or with lvm2 etc... are usually using MiB, GiB and TiB.


Show the built-in help message and exit.
Metadata profile, values like for data profile.
Data profile, raid0, raid1, raid5, raid6, raid10, dup or single.
Use mixed block groups (data and metadata profile must match).
Data to metadata ratio, e.g. 200 (the default), which means allocate 0.5% for metadata. Setting this ratio only makes sense for non-mixed filesystems. When using this option in combination with -M, it will be ignored.


This program is an example of what can be done using the python-btrfs library.

Source and documentation on github: