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 15.15.3 File Space Management
 -----------------------------
 
 The data files you define in the configuration file form the tablespace
 of `InnoDB'. The files are simply concatenated to form the tablespace.
 There is no striping in use.  Currently you cannot define where in the
 tablespace your tables will be allocated. However, in a newly created
 tablespace, `InnoDB' allocates space starting from the first data file.
 
 The tablespace consists of database pages with a default size of 16KB.
 The pages are grouped into extents of 64 consecutive pages. The "files"
 inside a tablespace are called segments in `InnoDB'.  The name of the
 "rollback segment" is somewhat confusing because it actually contains
 many segments in the tablespace.
 
 Two segments are allocated for each index in `InnoDB'.  One is for
 non-leaf nodes of the B-tree, the other is for the leaf nodes. The idea
 here is to achieve better sequentiality for the leaf nodes, which
 contain the data.
 
 When a segment grows inside the tablespace, `InnoDB' allocates the
 first 32 pages to it individually. After that `InnoDB' starts to
 allocate whole extents to the segment.  `InnoDB' can add to a large
 segment up to 4 extents at a time to ensure good sequentiality of data.
 
 Some pages in the tablespace contain bitmaps of other pages, and
 therefore a few extents in an `InnoDB' tablespace cannot be allocated
 to segments as a whole, but only as individual pages.
 
 When you ask for available free space in the tablespace by issuing a
 `SHOW TABLE STATUS', `InnoDB' reports the extents that are definitely
 free in the tablespace.  `InnoDB' always reserves some extents for
 clean-up and other internal purposes; these reserved extents are not
 included in the free space.
 
 When you delete data from a table, `InnoDB' will contract the
 corresponding B-tree indexes. It depends on the pattern of deletes
 whether that frees individual pages or extents to the tablespace, so
 that the freed space becomes available for other users. Dropping a
 table or deleting all rows from it is guaranteed to release the space
 to other users, but remember that deleted rows will be physically
 removed only in an (automatic) purge operation after they are no longer
 needed in transaction rollback or consistent read.
 

Info Catalog

(mysql.info.gz) InnoDB Raw Devices

(mysql.info.gz) File space management

(mysql.info.gz) InnoDB File Defragmenting