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Device Mapper
The device mapper is a framework provided by the Linux kernel for mapping physical block devices onto higher-level ''virtual block devices''. It forms the foundation of the logical volume manager (LVM), software RAIDs and dm-crypt disk encryption, and offers additional features such as file system snapshots. Device mapper works by passing data from a virtual block device, which is provided by the device mapper itself, to another block device. Data can be also modified in transition, which is performed, for example, in the case of device mapper providing disk encryption or simulation of unreliable hardware behavior. This article focuses on the device mapper implementation in the Linux kernel, but the device mapper functionality is also available in both NetBSD and DragonFly BSD. Usage Applications (like LVM2 and Enterprise Volume Management System (EVMS)) that need to create new mapped devices talk to the device mapper via the libdevmapper.so shared library, which in tur ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Software Framework
In computer programming, a software framework is a software abstraction that provides generic functionality which developers can extend with custom code to create applications. It establishes a standard foundation for building and deploying software, offering reusable components and design patterns that handle common programming tasks within a larger software platform or environment. Unlike libraries where developers call functions as needed, frameworks implement inversion of control by dictating program structure and calling user code at specific points, while also providing default behaviors, structured extensibility mechanisms, and maintaining a fixed core that accepts extensions without direct modification. Frameworks also differ from regular applications that can be modified (like web browsers through extensions, video games through mods), in that frameworks are intentionally incomplete scaffolding meant to be extended through well-defined extension points and followin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
The Linux Storage Stack Diagram
''The'' is a grammatical article in English, denoting nouns that are already or about to be mentioned, under discussion, implied or otherwise presumed familiar to listeners, readers, or speakers. It is the definite article in English. ''The'' is the most frequently used word in the English language; studies and analyses of texts have found it to account for seven percent of all printed English-language words. It is derived from gendered articles in Old English which combined in Middle English and now has a single form used with nouns of any gender. The word can be used with both singular and plural nouns, and with a noun that starts with any letter. This is different from many other languages, which have different forms of the definite article for different genders or numbers. Pronunciation In most dialects, "the" is pronounced as (with the voiced dental fricative followed by a schwa) when followed by a consonant sound, and as (homophone of the archaic pronoun ''thee'' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hybrid Drive
A hybrid drive (solid state hybrid drive – SSHD, and dual-storage drive) is a logical or physical computer storage device that combines a faster storage medium such as solid-state drive (SSD) with a higher-capacity hard disk drive (HDD). The intent is adding some of the speed of SSDs to the cost-effective storage capacity of traditional HDDs. The purpose of the SSD in a hybrid drive is to act as a cache for the data stored on the HDD, improving the overall performance by keeping copies of the most frequently used data on the faster SSD drive. There are two main configurations for implementing hybrid drives: dual-drive hybrid systems and solid-state hybrid drives. In dual-drive hybrid systems, physically separate SSD and HDD devices are installed in the same computer, having the data placement optimization performed either manually by the end user, or automatically by the operating system through the creation of a "hybrid" logical device. In solid-state hybrid drives, SSD an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Linux Unified Key Setup
The Linux Unified Key Setup (LUKS) is a disk encryption specification created by Clemens Fruhwirth in 2004 and originally intended for Linux. LUKS implements a platform-independent standard on-disk format for use in various tools. This facilitates compatibility and interoperability among different programs and operating systems, and assures that they all implement password management in a secure and documented manner. Description LUKS is used to encrypt a block device. The contents of the encrypted device are arbitrary, and therefore any filesystem can be encrypted, including swap partitions. There is an unencrypted header at the beginning of an encrypted volume, which allows up to 8 (LUKS1) or 32 (LUKS2) encryption keys to be stored along with encryption parameters such as cipher type and key size. The presence of this header is a major difference between LUKS and dm-crypt, since the header allows multiple different passphrases to be used, with the ability to change and rem ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cryptsetup
dm-crypt is a transparent block device encryption subsystem in Linux kernel versions 2.6 and later and in DragonFly BSD. It is part of the device mapper (dm) infrastructure, and uses cryptographic routines from the kernel's Crypto API. Unlike its predecessor cryptoloop, dm-crypt was designed to support advanced modes of operation, such as XTS, LRW and ESSIV, in order to avoid watermarking attacks. In addition to that, dm-crypt addresses some reliability problems of cryptoloop. dm-crypt is implemented as a device mapper target and may be stacked on top of other device mapper transformations. It can thus encrypt whole disks (including removable media), partitions, software RAID volumes, logical volumes, as well as files. It appears as a block device, which can be used to back file systems, swap or as an LVM physical volume. Some Linux distributions support the use of dm-crypt on the root file system. These distributions use initrd to prompt the user to enter a passphrase ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mdadm
mdadm is a Linux utility used to manage and monitor software RAID devices. It is used in modern Linux distributions in place of older software RAID utilities such as raidtools2 or raidtools. mdadm is free software originally maintained by, and copyrighted to, Neil Brown of SUSE S.A., SUSE, and licensed under the terms of version 2 or later of the GNU General Public License. Name The name is derived from the ''md'' (multiple device) device nodes it ''administers'' or manages, and it replaced a previous utility ''mdctl''. The original name was "Mirror Disk", but was changed as more functions were added. The name is now understood to be short for Multiple Disk and Device Management. Overview Linux software RAID configurations can include anything presented to the Linux kernel as a block device. This includes whole hard drives (for example, ), and their Disk partitioning, partitions (for example, ). RAID configurations * ''RAID 0'' – Block-level Data strip ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Software RAID
RAID (; redundant array of inexpensive disks or redundant array of independent disks) is a data storage virtualization technology that combines multiple physical data storage components into one or more logical units for the purposes of data redundancy, performance improvement, or both. This is in contrast to the previous concept of highly reliable mainframe disk drives known as ''single large expensive disk'' (''SLED''). Data is distributed across the drives in one of several ways, referred to as RAID levels, depending on the required level of redundancy and performance. The different schemes, or data distribution layouts, are named by the word "RAID" followed by a number, for example RAID 0 or RAID 1. Each scheme, or RAID level, provides a different balance among the key goals: reliability, availability, performance, and capacity. RAID levels greater than RAID 0 provide protection against unrecoverable sector read errors, as well as against failures of whole phy ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Multipath I/O
In computer storage, multipath I/O is a fault-tolerance and performance-enhancement technique that defines more than one physical path between the Central processing unit, CPU in a computer system and its mass storage, mass-storage devices through the Computer bus, buses, controllers, switches, and bridge devices connecting them. As an example, a SCSI hard disk drive may connect to two SCSI Disk controller, controllers on the same computer, or a disk may connect to two Fibre Channel ports. Should one controller, port or switch fail, the operating system can route the Input/output, I/O through the remaining controller, port or switch transparently and with no changes visible to the applications, other than perhaps resulting in increased Latency (engineering), latency. Multipath software layers can leverage the redundant paths to provide performance-enhancing features, including dynamic load balancing (computing), load balancing, traffic shaping, automatic path management, and dyna ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Linux DM Multipath
Device Mapper Multipath Input Output (DM-MPIO) or DM-Multipathing provides input/output (I/O) fail-over and load-balancing by using multipath I/O within Linux for block devices. By utilizing device-mapper, the multipathd daemon provides the host-side logic to use multiple paths of a redundant network to provide continuous availability and higher-bandwidth connectivity between the host server and the block-level device. DM-MPIO handles the rerouting of block I/O to an alternate path in the event of a path failure. DM-MPIO can also balance the I/O load across all of the available paths that are typically utilized in Fibre Channel (FC) and iSCSI SAN environments. DM-MPIO is based on the device mapper, which provides the basic framework that maps one block device onto another. Considerations When utilizing Linux DM-MPIO in a datacenter that has other operating systems and multipath solutions, key components of path management must be considered. *Load balancing — The worklo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Disk Mirroring
In Data storage device, data storage, disk mirroring is the Replication (computing), replication of logical disk volumes onto separate physical hard disks in Real-time computing, real time to ensure continuous availability. It is most commonly used in RAID 1. A mirrored volume is a complete logical representation of separate volume copies. In a IT disaster recovery, disaster recovery context, mirroring data over long distance is referred to as storage replication. Depending on the technologies used, replication can be performed synchronously, Asynchronous communication, asynchronously, semi-synchronously, or point-in-time. Replication is enabled via microcode on the disk array controller or via Server (computing), server software. It is typically a proprietary solution, not compatible between various data storage device vendors. Mirroring is typically only synchronous. Synchronous writing typically achieves a recovery point objective (RPO) of zero lost data. Asynchronous replica ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hard Disk Drive
A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating hard disk drive platter, platters coated with magnetic material. The platters are paired with disk read-and-write head, magnetic heads, usually arranged on a moving actuator arm, which read and write data to the platter surfaces. Data is accessed in a random-access manner, meaning that individual Block (data storage), blocks of data can be stored and retrieved in any order. HDDs are a type of non-volatile storage, retaining stored data when powered off. Modern HDDs are typically in the form of a small disk enclosure, rectangular box. Hard disk drives were introduced by IBM in 1956, and were the dominant secondary storage device for History of general-purpose CPUs, general-purpose computers beginning in the early 1960s. HDDs maintained this position into the modern er ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Solid-state Drive
A solid-state drive (SSD) is a type of solid-state storage device that uses integrated circuits to store data persistently. It is sometimes called semiconductor storage device, solid-state device, or solid-state disk. SSDs rely on non-volatile memory, typically NAND flash, to store data in memory cells. The performance and endurance of SSDs vary depending on the number of bits stored per cell, ranging from high-performing single-level cells (SLC) to more affordable but slower quad-level cells (QLC). In addition to flash-based SSDs, other technologies such as 3D XPoint offer faster speeds and higher endurance through different data storage mechanisms. Unlike traditional hard disk drives (HDDs), SSDs have no moving parts, allowing them to deliver faster data access speeds, reduced latency, increased resistance to physical shock, lower power consumption, and silent operation. Often interfaced to a system in the same way as HDDs, SSDs are used in a variety of devices, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
