Block suballocationBlock suballocation is a feature of some computer s which allows large blocks or allocation units to be used while making efficient use of empty space at the end of large files, space which would otherwise be lost for other use to internal fragmentation. In file systems that don't support fragments, this feature is also called tail merging or tail packing because it is commonly done by packing the "tail", or last partial block, of multiple files into a single block.
Extended file attributesExtended file attributes are features that enable users to associate s with metadata not interpreted by the filesystem, whereas regular attributes have a purpose strictly defined by the filesystem (such as or records of creation and modification times). Unlike , which can usually be as large as the maximum file size, extended attributes are usually limited in size to a value significantly smaller than the maximum file size.
ReiserFSReiserFS is a general-purpose, initially designed and implemented by a team at Namesys led by Hans Reiser and licensed under GPLv2. Introduced in version 2.4.1 of the Linux kernel, it was the first journaling file system to be included in the standard kernel. ReiserFS was the default file system in Novell's SUSE Linux Enterprise until Novell decided to move to ext3 on October 12, 2006, for future releases. Namesys considered ReiserFS version 3.
SquashFSSquashfs is a compressed read-only for Linux. Squashfs compresses , inodes and , and supports block sizes from 4 KiB up to 1 MiB for greater compression. Several compression algorithms are supported. Squashfs is also the name of free software, licensed under the GPL, for accessing Squashfs filesystems. Squashfs is intended for general read-only file-system use and in constrained block-device memory systems (e.g. embedded systems) where low overhead is needed.
Comparison of file systemsThe following tables compare general and technical information for a number of . Note that in addition to the below table, block capabilities can be implemented below the file system layer in Linux (LVM, , cryptsetup) or Windows (Volume Shadow Copy Service, SECURITY), etc. "online" and "offline" are synonymous with "mounted" and "not mounted". While storage devices usually have their size expressed in powers of 10 (for instance a 1 TB Solid State Drive will contain at least 1,000,000,000,000 (1012, 10004) bytes), filesystem limits are invariably powers of 2, so usually expressed with IEC prefixes.
ZFSZFS (previously: Zettabyte File System) is a with volume management capabilities. It began as part of the Sun Microsystems Solaris operating system in 2001. Large parts of Solaris – including ZFS – were published under an open source license as OpenSolaris for around 5 years from 2005, before being placed under a closed source license when Oracle Corporation acquired Sun in 20092010. During 2005 to 2010, the open source version of ZFS was ported to Linux, Mac OS X (continued as MacZFS) and FreeBSD.
Ext4ext4 (fourth extended filesystem) is a for Linux, developed as the successor to ext3. ext4 was initially a series of backward-compatible extensions to ext3, many of them originally developed by Cluster File Systems for the between 2003 and 2006, meant to extend storage limits and add other performance improvements. However, other Linux kernel developers opposed accepting extensions to ext3 for stability reasons, and proposed to fork the source code of ext3, rename it as ext4, and perform all the development there, without affecting existing ext3 users.
Reiser4Reiser4 is a computer , successor to the ReiserFS file system, developed from scratch by Namesys and sponsored by DARPA as well as Linspire. Reiser4 was named after its former lead developer Hans Reiser. , the Reiser4 patch set is still being maintained, but according to Phoronix, it is unlikely to be merged into mainline Linux without corporate backing.
Ext3ext3, or third extended filesystem, is a that is commonly used by the Linux kernel. It used to be the default for many popular Linux distributions. Stephen Tweedie first revealed that he was working on extending ext2 in Journaling the Linux ext2fs Filesystem in a 1998 paper, and later in a February 1999 kernel mailing list posting. The filesystem was merged with the mainline Linux kernel in November 2001 from 2.4.15 onward. Its main advantage over ext2 is , which improves reliability and eliminates the need to check the file system after an unclean shutdown.
Copy-on-writeCopy-on-write (COW), sometimes referred to as implicit sharing or shadowing, is a resource-management technique used in computer programming to efficiently implement a "duplicate" or "copy" operation on modifiable resources. If a resource is duplicated but not modified, it is not necessary to create a new resource; the resource can be shared between the copy and the original. Modifications must still create a copy, hence the technique: the copy operation is deferred until the first write.
