btrfs-space-calculator - Man Page

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, while partitions created in your average partition table or with lvm2 etc... are usually using MiB, GiB and TiB.

-h,  --help

Show the built-in help message and exit.

-m,  --metadata PROFILE

Metadata profile, values like for data profile.

-d,  --data PROFILE

Data profile, raid0, raid1, raid5, raid6, raid10, dup or single.

-M,  --mixed

Use mixed block groups (data and metadata profile must match).

-r,  --ratio RATIO

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: https://github.com/knorrie/python-btrfs