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Extent (file systems)
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<h2 id="adoption">Adoption</h2> <p>The systems supporting file system extents include the following: </p> <ul><li><a href="/facts/Apple_File_System/y16sIvSM">APFS</a> – Apple File System</li> <li><a href="/facts/Automatic_Storage_Management/cJUEFBwS">ASM</a> – Automatic Storage Management – <a href="/facts/Oracle_Corporation/0z14FygH">Oracle's</a> database-oriented file system</li> <li><a href="/facts/Be_File_System/fQ5uUJj9">BFS</a> – <a href="/facts/BeOS/tGYfe835">BeOS</a>, <a href="/facts/Magnussoft_ZETA/9tkr4Bak">Zeta</a> and <a href="/facts/Haiku_(operating_system)/0urtHJxC">Haiku</a> operating systems</li> <li><a href="/facts/Btrfs/lPwmXVJ6">Btrfs</a> – Extent-based <a href="/facts/Copy-on-write/Vz5V8uMX">copy-on-write</a> (COW) file system for Linux</li> <li>EFS – Extent File System – <a href="/facts/Silicon_Graphics/DKvkrfLX">SGI's</a> first-generation file system for <a href="/facts/IRIX/vK9rSatM">IRIX</a></li> <li><a href="/facts/Ext4/zFbQRpsh">ext4</a> – <a href="/facts/Linux_kernel/dlkduHuA">Linux</a> file system (when the configuration enables extents – the default in Linux since version 2.6.23)</li> <li><a href="/facts/Files-11/oXRKHxRE">Files-11</a> – <a href="/facts/OpenVMS/rAnHAgpD">OpenVMS</a> file system</li> <li><a href="/facts/Hierarchical_File_System_(Apple)/FVv6r1pe">HFS</a> and <a href="/facts/HFS_Plus/sWk14kM5">HFS Plus</a> – Hierarchical File System – <a href="/facts/Apple_Inc./oTJYta3k">Apple</a> <a href="/facts/Macintosh/8GhnXTK0">Macintosh</a> file systems</li> <li><a href="/facts/High_Performance_File_System/dz2Vgek4">High Performance File System</a> (HPFS) – on <a href="/facts/OS%2f2/uVBl6ItP">OS/2</a>, <a href="/facts/EComStation/0FseHaUf">eComStation</a> and <a href="/facts/ArcaOS/KGRJJQTA">ArcaOS</a></li> <li>IceFS – IceFileSystem – optional file system for <a href="/facts/MorphOS/xWSeUeWM">MorphOS</a></li> <li><a href="/facts/IBM_Journaled_File_System_2_(JFS2)/bmJLqaP8">JFS</a> – Journaled File System – used by <a href="/facts/AIX_(operating_system)/cRWERua2">AIX</a>, <a href="/facts/OS%2f2/uVBl6ItP">OS/2</a>/eComStation/ArcaOS and <a href="/facts/Linux/9FvCKSTq">Linux</a> operating systems</li> <li><a href="/facts/ISO_9660/zAEVMFnu">ISO 9660</a> – Extent-based file system for optical disc media</li> <li>MPE File System – the file system of the <a href="/facts/Multi-Programming_Executive/sqWtI9Qh">Multi-Programming Executive</a> operating system.</li> <li><a href="/facts/NTFS/dryNM3BK">NTFS</a> – used by Windows</li> <li><a href="/facts/OCFS2/Hh7UcTvl">OCFS2</a> – Oracle Cluster File System – a <a href="/facts/Shared-disk_file_system/Bz61f7Ce">shared-disk file system</a> for Linux</li> <li><a href="/facts/Reiser4/lB99Gq3d">Reiser4</a> – Linux file system (in "extents" mode)</li> <li><a href="/facts/SINTRAN_III/fcstYeLQ">SINTRAN III</a> – file system used by early computer company <a href="/facts/Norsk_Data/7QK0WYJk">Norsk Data</a></li> <li><a href="/facts/Universal_Disk_Format/QwlH2aPR">UDF</a> – Universal Disk Format – standard for optical media</li> <li><a href="/facts/VERITAS_File_System/qh1rtMTQ">VERITAS File System</a> – enabled via the pre-allocation API and CLI</li> <li><a href="/facts/XFS/2I4Wn5wG">XFS</a> – <a href="/facts/Silicon_Graphics/DKvkrfLX">SGI's</a> second-generation file system for <a href="/facts/IRIX/vK9rSatM">IRIX</a> and <a href="/facts/Linux/9FvCKSTq">Linux</a></li></ul> <p>Adoption outside of file systems include the following: </p> <ul><li><a href="/facts/Microsoft_SQL_Server/eCdt2JBL">Microsoft SQL Server</a> – versions support 64 KB extents consisting of eight 8 KB pages.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a></li> <li><a href="/facts/Oracle_Database/FHv5g732">Oracle Database</a> groups blocks into extents and extents into segments.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a></li></ul> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Comparison_of_file_systems/M7ynsI2z">Comparison of file systems</a></li></ul> <h2 id="external-links">External links</h2> Look up <i>extent</i> in Wiktionary, the free dictionary. <ul><li><a href="http://sunsite.uakom.sk/sunworldonline/swol-05-1999/swol-05-filesystem.html">Getting to know the Solaris filesystem, Part 1</a>: Allocation and storage strategy – a comparison of block-based and extent-based allocation</li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>"Understanding Ext4 (part1): Extents". 2010-12-20. Archived from the original on 2015-02-03. Retrieved 2015-02-02. What's really a departure for EXT4 however, is the use of extents rather than the old, inefficient indirect block mechanism used by earlier Unix file systems (e.g. EXT2 and EXT3) for tracking file content. Extents are similar to cluster runs in the NTFS file system; essentially, they specify an initial block address and the number of blocks that make up the extent. A file that is fragmented will have multiple extents, but EXT4 tries very hard to keep files contiguous. <a href="https://web.archive.org/web/20150203015625/http://digital-forensics.sans.org/blog/2010/12/20/digital-forensics-understanding-ext4-part-1-extents" target="_blank">https://web.archive.org/web/20150203015625/http://digital-forensics.sans.org/blog/2010/12/20/digital-forensics-understanding-ext4-part-1-extents</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>"Ext4 Disk Layout". 2015-01-26. Retrieved 2015-02-02. If flex_bg is enabled, it is possible to allocate very large files with a single extent, at a considerable reduction in metadata block use, and some improvement in disk efficiency. <a href="https://ext4.wiki.kernel.org/index.php/Ext4_Disk_Layout#Extent_Tree" target="_blank">https://ext4.wiki.kernel.org/index.php/Ext4_Disk_Layout#Extent_Tree</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>"Pages and Extents Architecture Guide - SQL Server". learn.microsoft.com. Microsoft. 12 June 2024. Retrieved 18 December 2024. <a href="https://learn.microsoft.com/en-us/sql/relational-databases/pages-and-extents-architecture-guide?view=sql-server-ver16" target="_blank">https://learn.microsoft.com/en-us/sql/relational-databases/pages-and-extents-architecture-guide?view=sql-server-ver16</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>"Oracle Database 23ai Technical Architecture". docs.oracle.com. Oracle Corporation. Retrieved 18 December 2024. <a href="https://docs.oracle.com/en/database/oracle/oracle-database/23/dbiad/all_diagrams.html" target="_blank">https://docs.oracle.com/en/database/oracle/oracle-database/23/dbiad/all_diagrams.html</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> </ol>