Editing ReiserFS (section)

==Design==
ReiserFS stores file metadata ("stat items"), [[Directory (computing)|directory]] entries ("directory items"), [[inode]] block lists ("indirect items"), and tails of [[computer file|files]] ("direct items") in a single, combined [[B+ tree]] keyed by a universal object ID. Disk blocks allocated to nodes of the tree are "formatted internal blocks".  Blocks for leaf nodes (in which items are packed end-to-end) are "formatted leaf blocks".  All other blocks are "unformatted blocks" containing file contents.  Directory items with too many entries or indirect items which are too long to fit into a node spill over into the right leaf neighbour. Block allocation is tracked by [[free space bitmap]]s in fixed locations.

By contrast, [[ext2]] and other Berkeley [[Unix File System|FFS]]-like file systems of that time simply used a fixed formula for computing inode locations, hence limiting the number of files they may contain.<ref>{{cite conference |author1=Mingming Cao |author2=Theodore Y. Ts'o |author2-link=Theodore Y. Ts'o |author3=Badari Pulavarty |author4=Suparna Bhattacharya |author4-link=Suparna Bhattacharya |date=2005-07-26 |title=State of the Art: Where we are with the Ext3 file system |publisher=IBM Linux Technology Center |book-title=2005 Linux Symposium |location=Ottawa, Canada |url=http://ext2.sourceforge.net/2005-ols/paper-html/node40.html |access-date=2007-03-08 }}</ref> Most such file systems also store directories as simple lists of entries, which makes directory lookups and updates [[Time complexity#Linear time|linear time]] operations and degrades performance on very large directories. The single [[B+ tree]] design in ReiserFS avoids both of these problems due to better scalability properties.