(
B-TRee 
File 
System)  An advanced Linux file system designed for the ultra-large storage requirements of the 21st century.  Btrfs features "copy-on-write" (COW), which makes a copy of the data when modified by another application or user, dynamic resizing, along with RAID, compression and snapshot support.  Also called "B-Tree FS," "Butter FS" and "Butterface."  For more information, visit http://btrfs.wiki.kernel.org.  See 
copy-on-write, 
RAID and 
file system.