Btrfs is a next generation Linux file system that offers advanced management, reliability, and scalability features. It is unique in offering snapshots, compression, and integrated device management.
Creating a btrfs File System
In order to make a basic btrfs file system, use the following command:
# mkfs. btrfs /dev/device
Here is one example:
# mkfs.btrfs -f /dev/mapper/LUN13
See http://btrfs.wiki.kernel.org for more information.
Turning ON incompat feature 'extref': increased hardlink limit per file to 65536
Turning ON incompat feature 'skinny-metadata': reduced-size metadata extent refs
fs created label (null) on /dev/mapper/LUN13
nodesize 16384 leafsize 16384 sectorsize 4096 size 1.50TiB
For more information on creating btrfs file systems with added devices and specifying multi-device profiles for metadata and data, refer to
Mounting a btrfs file system
To mount any device in the btrfs file system use the following command:
# mount /dev/device /mount-point
Other useful mount options include:
Appending this option to the mount command tells btrfs to scan the named device for a btrfs volume. This is used to ensure the mount will succeed as attempting to mount devices that are not btrfs will cause the mount to fail.
Note: This does not mean all devices will be added to the file system, it only scans them.
Use this option to set the maximum amount of space (in bytes) that can be used to inline data within a metadata B-tree leaf. The default is 8192 bytes. For 4k pages it is limited to 3900 bytes due to additional headers that need to fit into the leaf.
alloc_start = number
Use this option to set where in the disk allocations start.
Use this option to assign the number of worker threads allocated.
Use this option to enable discard/TRIM on freed blocks.
Use this option to disable the use of ACL's.
Use this option to store the free space data on disk to make caching a block group faster.
This is a persistent change and is safe to boot into old kernels.
Use this option to disable the above space_cache.
Use this option to clear all the free space caches during mount. This is a safe option but will trigger the space cache to be rebuilt. As such, leave the file system mounted in order to let the rebuild process finish. This mount option is intended to be used once and only after problems are apparent with the free space.
This option is used to debug problems with " no space left" .
Use this option to enable autorecovery upon mount.