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Log-structured File System
A log-structured filesystem is a file system in which data and metadata are written sequentially to a circular buffer, called a log. The design was first proposed in 1988 by John K. Ousterhout and Fred Douglis and first implemented in 1992 by Ousterhout and Mendel Rosenblum for the Unix-like Sprite distributed operating system. Rationale Conventional file systems tend to lay out files with great care for spatial locality and make in-place changes to their data structures in order to perform well on optical and magnetic disks, which tend to seek relatively slowly. The design of log-structured file systems is based on the hypothesis that this will no longer be effective because ever-increasing memory sizes on modern computers would lead to I/O becoming write-heavy because reads would be almost always satisfied from memory cache. A log-structured file system thus treats its storage as a circular log and writes sequentially to the head of the log. This has several important sid ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
File System
In computing, file system or filesystem (often abbreviated to fs) is a method and data structure that the operating system uses to control how data is stored and retrieved. Without a file system, data placed in a storage medium would be one large body of data with no way to tell where one piece of data stopped and the next began, or where any piece of data was located when it was time to retrieve it. By separating the data into pieces and giving each piece a name, the data are easily isolated and identified. Taking its name from the way a paper-based data management system is named, each group of data is called a "file". The structure and logic rules used to manage the groups of data and their names is called a "file system." There are many kinds of file systems, each with unique structure and logic, properties of speed, flexibility, security, size and more. Some file systems have been designed to be used for specific applications. For example, the ISO 9660 file system is designe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Versioning File System
A versioning file system is any computer file system which allows a computer file to exist in several versions at the same time. Thus it is a form of revision control. Most common versioning file systems keep a number of old copies of the file. Some limit the number of changes per minute or per hour to avoid storing large numbers of trivial changes. Others instead take periodic snapshots whose contents can be accessed with similar semantics to normal file access. Similar technologies Backup A versioning file system is similar to a periodic backup, with several key differences. * Backups are normally triggered on a timed basis, while versioning occurs when the file changes. * Backups are usually system-wide or partition-wide, while versioning occurs independently on a file-by-file basis. * Backups are normally written to separate media, while versioning file systems write to the same hard drive (and normally the same folder, directory, or local partition). In comparison to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Computer File Systems
A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations (computation) automatically. Modern digital electronic computers can perform generic sets of operations known as programs. These programs enable computers to perform a wide range of tasks. A computer system is a nominally complete computer that includes the hardware, operating system (main software), and peripheral equipment needed and used for full operation. This term may also refer to a group of computers that are linked and function together, such as a computer network or computer cluster. A broad range of industrial and consumer products use computers as control systems. Simple special-purpose devices like microwave ovens and remote controls are included, as are factory devices like industrial robots and computer-aided design, as well as general-purpose devices like personal computers and mobile devices like smartphones. Computers power the Internet, which links bil ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Comparison Of File Systems
The following tables compare general and technical information for a number of file systems. General information Limits Metadata Features File capabilities Block capabilities Note that in addition to the below table, block capabilities can be implemented below the file system layer in Linux ( LVM, integritysetup, cryptsetup) or Windows (Volume Shadow Copy Service, SECURITY), etc. Resize capabilities "online" and "offline" are synonymous with "mounted" and "not mounted". Allocation and layout policies OS support See also * List of file systems * Comparison of file archivers * List of archive formats * Comparison of archive formats Notes References External links A speed comparison of filesystems on Linux 2.4.5(archived) Filesystems (ext3, reiser, xfs, jfs) comparison on Debian Etch{{Webarchive, url=https://web.archive.org/web/20180304191727/https://debian-administration.org/article/388/Filesystems_ext3_reiser_xfs_jfs_comparison ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
List Of Log-structured File Systems
This is an incomplete list of log-structured file system implementations. * James T, Brady while in IBM Poughkeepsie Lab conceived a log structured paging file system in 1979 which was implemented in MVS SP2 in 1980."1981 IBM Corporate Technical Recognition Event Book, Outstanding Innovation Award, “Virtual Storage Disk Paging”" * John K. Ousterhout and Mendel Rosenblum implemented the first log-structured file system for the Sprite operating system in 1992.Rosenblum, Mendel and Ousterhout, John K. (June 1990) -The LFS Storage Manager. ''Proceedings of the 1990 Summer Usenix''. pp315-324.Rosenblum, Mendel and Ousterhout, John K. (February 1992) -. ''ACM Transactions on Computer Systems, Vol. 10 Issue 1''. pp26-52. * BSD-LFS, an implementation by Margo Seltzer was added to 4.4BSD, and was later ported to 386BSD. It lacked support for snapshots. It was removed from FreeBSD and OpenBSD, but still lives on in NetBSD. * Plan 9's Fossil file system is also log-structured and supp ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fragmentation (computer)
In computer storage, fragmentation is a phenomenon in which storage space, main storage or secondary storage, is used inefficiently, reducing capacity or performance and often both. The exact consequences of fragmentation depend on the specific system of storage allocation in use and the particular form of fragmentation. In many cases, fragmentation leads to storage space being "wasted", and in that case the term also refers to the wasted space itself. Basic principle When a computer program requests blocks of memory from the computer system, the blocks are allocated in chunks. When the computer program is finished with a chunk, it can free it back to the system, making it available to later be allocated again to another or the same program. The size and the amount of time a chunk is held by a program varies. During its lifespan, a computer program can request and free many chunks of memory. When a program is started, the free memory areas are long and contiguous. Over time and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Design Rationale
A design rationale is an explicit documentation of the reasons behind decisions made when designing a system or artifact. As initially developed by W.R. Kunz and Horst Rittel, design rationale seeks to provide argumentation-based structure to the political, collaborative process of addressing wicked problems. Overview A design rationale is the explicit listing of decisions made during a design process, and the reasons why those decisions were made.Jarczyk, Alex P.; Löffler, Peter; Shipman III, Frank M. (1992), "Design Rationale for Software Engineering: A Survey", ''25th Hawaii International Conference on System Sciences'', 2, pp. 577-586 Its primary goal is to support designers by providing a means to record and communicate the argumentation and reasoning behind the design process.Horner, J.; Atwood, M.E. (2006), "Effective Design Rationale: Understanding the Barriers", in Dutoit, A.H.; McCall, R.; Mistrík, I. et al., Rationale Management in Software Engineering, Springer ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Write Amplification
Write amplification (WA) is an undesirable phenomenon associated with flash memory and solid-state drives (SSDs) where the actual amount of information physically written to the storage media is a multiple of the logical amount intended to be written. Because flash memory must be erased before it can be rewritten, with much coarser granularity of the erase operation when compared to the write operation, the process to perform these operations results in moving (or rewriting) user data and metadata more than once. Thus, rewriting some data requires an already-used-portion of flash to be read, updated, and written to a new location, together with initially erasing the new location if it was previously used at some point in time. Due to the way flash works, much larger portions of flash must be erased and rewritten than actually required by the amount of new data. This multiplying effect increases the number of writes required over the life of the SSD, which shortens the time it ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Garbage Collection (computer Science)
In computer science, garbage collection (GC) is a form of automatic memory management. The ''garbage collector'' attempts to reclaim memory which was allocated by the program, but is no longer referenced; such memory is called '' garbage''. Garbage collection was invented by American computer scientist John McCarthy around 1959 to simplify manual memory management in Lisp. Garbage collection relieves the programmer from doing manual memory management, where the programmer specifies what objects to de-allocate and return to the memory system and when to do so. Other, similar techniques include stack allocation, region inference, and memory ownership, and combinations thereof. Garbage collection may take a significant proportion of a program's total processing time, and affect performance as a result. Resources other than memory, such as network sockets, database handles, windows, file descriptors, and device descriptors, are not typically handled by garbage collection, but ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Snapshot (computer Storage)
In computer systems, a snapshot is the state of a system at a particular point in time. The term was coined as an analogy to that in photography. It can refer to an actual copy of the state of a system or to a capability provided by certain systems. Rationale A full backup of a large data set may take a long time to complete. On multi-tasking or multi-user systems, there may be writes to that data while it is being backed up. This prevents the backup from being atomic and introduces a version skew that may result in data corruption. For example, if a user moves a file into a directory that has already been backed up, then that file would be completely missing on the backup media, since the backup operation had already taken place before the addition of the file. Version skew may also cause corruption with files which change their size or contents underfoot while being read. One approach to safely backing up live data is to temporarily disable write access to data during t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Circular Buffer
In computer science, a circular buffer, circular queue, cyclic buffer or ring buffer is a data structure that uses a single, fixed-size buffer as if it were connected end-to-end. This structure lends itself easily to buffering data streams. There were early circular buffer implementations in hardware. Overview A circular buffer first starts out empty and has a set length. In the diagram below is a 7-element buffer: : Assume that 1 is written in the center of a circular buffer (the exact starting location is not important in a circular buffer): : Then assume that two more elements are added to the circular buffer — 2 & 3 — which get put after 1: : If two elements are removed, the two oldest values inside of the circular buffer would be removed. Circular buffers use FIFO (''first in, first out'') logic. In the example, 1 & 2 were the first to enter the circular buffer, they are the first to be removed, leaving 3 inside of the buffer. : If the buffer has 7 ele ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Shingled Magnetic Recording
Shingled magnetic recording (SMR) is a magnetic storage data recording technology used in hard disk drives (HDDs) to increase storage density and overall per-drive storage capacity. Conventional hard disk drives record data by writing non-overlapping magnetic tracks parallel to each other (perpendicular magnetic recording, PMR), while shingled recording writes new tracks that overlap part of the previously written magnetic track, leaving the previous track narrower and allowing for higher track density. Thus, the tracks partially overlap similar to roof shingles. This approach was selected because, if the writing head is made too narrow, it cannot provide the very high fields required in the recording layer of the disk. The overlapping-tracks architecture complicates the writing process since writing to one track also overwrites an adjacent track. If adjacent tracks contain valid data, they must be rewritten as well. As a result, SMR drives are divided into many append-only (seq ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
