What is RAID redundant array of independent disks RAID redundant array of independent disks originally redundant array of inexpensive disks is a way of storing the same data in different places on multiple hard disks to protect data in the case of a drive failure. However, not all RAID levels provide redundancy. By submitting your personal information, you agree that Tech. Target and its partners may contact you regarding relevant content, products and special offers. You also agree that your personal information may be transferred and processed in the United States, and that you have read and agree to the Terms of Use and the Privacy Policy. Convolution is the most important method to analyze signals in digital signal processing. It describes how to convolve singals in 1D and 2D. Kernel Definition In ChemistryThe kernel is the central module of an operating system. It is the part of the operating system that loads first, and it remains in main memory. Kernel Definition ComputerHistory of RAIDThe term RAID was coined in 1. David Patterson, Randy Katz and Garth A. Gibson. In their 1. A Case for Redundant Arrays of Inexpensive Disks RAID, the three argued that an array of inexpensive drives could beat the performance of the top disk drives of the time. By utilizing redundancy, a RAID array could be more reliable than any one disk drive. The kernel is a program that constitutes the central core of a computer operating system. It has complete control over everything that occurs in the system. STAT2 Linux Programmers Manual STAT2 NAME top stat, fstat, lstat, fstatat get file status SYNOPSIS top. While this report was the first to put a name to the concept, the use of redundant disks was already being discussed by others. Geac Computer Corp. Gus German and Ted Grunau first referred to this idea as MF 1. IBMs Norman Ken Ouchi filed a patent in 1. RAID 4. In 1. 98. Digital Equipment Corp. Kernel Definition Of' title='2 6 Kernel Definition Of' />RAID 1, and in 1. IBM patent was filed for what would become RAID 5. Patterson, Katz and Gibson also looked at what was being done by companies such as Tandem Computers, Thinking Machines and Maxstor to define their RAID taxonomies. While the levels of RAID listed in the 1. RAID array products. According to Katz, the term inexpensive in the acronym was soon replaced with independent by industry vendors due to the implications of low costs. How RAID works. RAID works by placing data on multiple disks and allowing inputoutput IO operations to overlap in a balanced way, improving performance. Because the use of multiple disks increases the mean time between failures MTBF, storing data redundantly also increases fault tolerance. RAID arrays appear to the operating system OS as a single logical hard disk. RAID employs the techniques of disk mirroring or disk striping. Mirroring copies identical data onto more than one drive. Striping partitions each drives storage space into units ranging from a sector 5. The stripes of all the disks are interleaved and addressed in order. Image of a five tray RAID hard drive. In a single user system where large records, such as medical or other scientific images, are stored, the stripes are typically set up to be small perhaps 5. In a multiuser system, better performance requires that you establish a stripe wide enough to hold the typical or maximum size record. Kernel mode, also referred to as system mode, is one of the two distinct modes of operation of the CPU central processing unit in Linux. The other is user mode, a. The programming guide to the CUDA model and interface. Linux Kernel 2. 6 using KAMEtools. This chapter explains the usage of the native IPsec stack of the Linux Kernel 2. The installation and the. OPEN2 Linux Programmers Manual OPEN2 NAME top open, openat, creat open and possibly create a file. Kernel Definitions' title='2 6 Kernel Definitions' />This allows overlapped disk IO across drives. Disk mirroring and disk striping can be combined on a RAID array. Mirroring and striping are used together in RAID 0. RAID 1. 0. RAID controller. A RAID controller can be used as a level of abstraction between the OS and the physical disks, presenting groups of disks as logical units. Using a RAID controller can improve performance and help protect data in case of a crash. A RAID controller can be used in both hardware and software based RAID arrays. In a hardware based RAID product, a physical controller manages the array. When in the form of a Peripheral Component Interconnect or PCI Express card, the controller can be designed to support drive formats such as SATA and SCSI. A physical RAID controller can also be part of the motherboard. With software based RAID, the controller uses the resources of the hardware system. While it performs the same functions as a hardware based RAID controller, software based RAID controllers may not enable as much of a performance boost. If a software based RAID implementation isnt compatible with a systems boot up process, and hardware based RAID controllers are too costly, firmware or driver based, RAID is another implementation option. A firmware based RAID controller chip is located on the motherboard, and all operations are performed by the CPU, similar to software based RAID. However, with firmware, the RAID system is only implemented at the beginning of the boot process. Once the OS has loaded, the controller driver takes over RAID functionality. A firmware RAID controller isnt as pricy as a hardware option, but puts more strain on the computers CPU. Firmware based RAID is also called hardware assisted software RAID, hybrid model RAID and fake RAID. RAID levels. In the 1. RAID, 0 through 5. How To Install Windowbuilder Eclipse Plugin Development. This numbered system allowed them to differentiate the versions and how they used redundancy and spread data across the array. The number of levels has since expanded and has been broken into three categories standard, nested and nonstandard RAID levels. Standard RAID levels. RAID 0 This configuration has striping, but no redundancy of data. It offers the best performance, but no fault tolerance. RAID 1 Also known as disk mirroring, this configuration consists of at least two drives that duplicate the storage of data. There is no striping. Read performance is improved since either disk can be read at the same time. Write performance is the same as for single disk storage. RAID 2 This configuration uses striping across disks, with some disks storing error checking and correcting ECC information. It has no advantage over RAID 3 and is no longer used. RAID 3 This technique uses striping and dedicates one drive to storing parity information. The embedded ECC information is used to detect errors. Data recovery is accomplished by calculating the exclusive OR XOR of the information recorded on the other drives. Since an IO operation addresses all the drives at the same time, RAID 3 cannot overlap IO. For this reason, RAID 3 is best for single user systems with long record applications. RAID 4 This level uses large stripes, which means you can read records from any single drive. This allows you to use overlapped IO for read operations. Since all write operations have to update the parity drive, no IO overlapping is possible. RAID 4 offers no advantage over RAID 5. RAID 5 This level is based on block level striping with parity. The parity information is striped across each drive, allowing the array to function even if one drive were to fail. The arrays architecture allows read and write operations to span multiple drives. This results in performance that is usually better than that of a single drive, but not as high as that of a RAID 0 array. RAID 5 requires at least three disks, but it is often recommended to use at least five disks for performance reasons. RAID 5 arrays are generally considered to be a poor choice for use on write intensive systems because of the performance impact associated with writing parity information. When a disk does fail, it can take a long time to rebuild a RAID 5 array. Performance is usually degraded during the rebuild time, and the array is vulnerable to an additional disk failure until the rebuild is complete. RAID 6 This technique is similar to RAID 5, but includes a second parity scheme that is distributed across the drives in the array. The use of additional parity allows the array to continue to function even if two disks fail simultaneously. However, this extra protection comes at a cost. RAID 6 arrays have a higher cost per gigabyte GB and often have slower write performance than RAID 5 arrays. Nested RAID levels. Linux manual page. OPEN2 Linux Programmers Manual OPEN2. SYNOPSIS         topinclude lt systypes. Feature Test Macro Requirements for glibc see featuretestmacros7. Since glibc 2. 1. POSIXCSOURCE 2. L. Before glibc 2. ATFILESOURCE. DESCRIPTION         top. The open system call opens the file specified by pathname. If the. specified file does not exist, it may optionally if OCREAT is. The return value of open is a file descriptor, a small, nonnegative. The file. descriptor returned by a successful call will be the lowest numbered. By default, the new file descriptor is set to remain open across an. FDCLOEXEC file descriptor flag described in. OCLOEXEC flag, described below. The file offset is set to the. A call to open creates a new open file description, an entry in the. The open file description records. A file. descriptor is a reference to an open file description this reference. For further details on open file. NOTES. The argument flags must include one of the following access modes. ORDONLY, OWRONLY, or ORDWR. These request opening the file read. In addition, zero or more file creation flags and file status flags. The file creation flags are OCLOEXEC. OCREAT, ODIRECTORY, OEXCL, ONOCTTY, ONOFOLLOW, OTMPFILE, and. OTRUNC. The file status flags are all of the remaining flags listed. The distinction between these two groups of flags is that the. IO operations. The file status flags can be retrieved. The full list of file creation flags and file status flags is as. OAPPEND. The file is opened in append mode. Before each write2, the. The modification of the file offset and the write. OAPPEND may lead to corrupted files on NFS filesystems if. This is. because NFS does not support appending to a file, so the. Enable signal driven IO generate a signal SIGIO by default. This feature is. available only for terminals, pseudoterminals, sockets, and. Linux 2. 6 pipes and FIFOs. See fcntl2 for further. See also BUGS, below. OCLOEXEC since Linux 2. Enable the close on exec flag for the new file descriptor. Specifying this flag permits a program to avoid additional. Four Winns Vista 268 Specifications For. FSETFD operations to set the FDCLOEXEC flag. Note that the use of this flag is essential in some. FSETFD operation to set the FDCLOEXEC flag does not suffice. Depending on the order of execution, the race. This kind of race is in. Linux system calls provide an equivalent of the. OCLOEXEC flag to deal with this problem. If pathname does not exist, create it as a regular file. The owner user ID of the new file is set to the effective. ID of the process. The group ownership group ID of the new file is set either. ID of the process System V semantics. ID of the parent directory BSD semantics. On Linux, the behavior depends on whether the set group ID. BSD semantics apply otherwise, System V semantics apply. For some filesystems, the behavior also depends on the. The mode argument specifies the file mode bits be applied when. This argument must be supplied when. OCREAT or OTMPFILE is specified in flags if neither OCREAT. OTMPFILE is specified, then mode is ignored. The. effective mode is modified by the processs umask in the usual. ACL, the mode of the created. Note that this mode applies only to. The following symbolic constants are provided for mode. SIRWXU 0. 07. 00 user file owner has read, write, and execute. SIRUSR 0. 04. 00 user has read permission. SIWUSR 0. 02. 00 user has write permission. SIXUSR 0. 01. 00 user has execute permission. SIRWXG 0. 00. 70 group has read, write, and execute permission. SIRGRP 0. 00. 40 group has read permission. SIWGRP 0. 00. 20 group has write permission. SIXGRP 0. 00. 10 group has execute permission. SIRWXO 0. 00. 07 others have read, write, and execute permission. SIROTH 0. 00. 04 others have read permission. SIWOTH 0. 00. 02 others have write permission. SIXOTH 0. 00. 01 others have execute permission. According to POSIX, the effect when other bits are set in mode. On Linux, the following bits are also honored. SISUID 0. 00. 40. ID bit. SISGID 0. ID bit see inode7. SISVTX 0. 00. 10. ODIRECT since Linux 2. Try to minimize cache effects of the IO to and from this. In general this will degrade performance, but it is. File IO is done directly tofrom user. The ODIRECT flag on its own makes an effort. OSYNC flag that data and necessary metadata. To guarantee synchronous IO, OSYNC must be. ODIRECT. See NOTES below for further. A semantically similar but deprecated interface for block. ODIRECTORY. If pathname is not a directory, cause the open to fail. This. flag was added in kernel version 2. FIFO or tape. device. Write operations on the file will complete according to the. IO data integrity completion. By the time write2 and similar return, the output data has. See NOTES below. OEXCL Ensure that this call creates the file if this flag is. OCREAT, and pathname already. EEXIST. When these two flags are specified, symbolic links are not. In general, the behavior of OEXCL is undefined if it is used. OCREAT. There is one exception on Linux 2. OEXCL can be used without OCREAT if pathname refers. If the block device is in use by the. EBUSY. On NFS, OEXCL is supported only when using NFSv. In NFS environments where OEXCL support. Portable. programs that want to perform atomic file locking using a. NFS support for. OEXCL, can create a unique file on the same filesystem e. PID, and use link2 to make a. If link2 returns 0, the lock is. Otherwise, use stat2 on the unique file to. OLARGEFILE. LFS Allow files whose sizes cannot be represented in an. The LARGEFILE6. 4SOURCE macro must be defined before. Setting the FILEOFFSETBITS feature test macro. OLARGEFILE is the preferred method. ONOATIME since Linux 2. Do not update the file last access time statime in the. This flag can be employed only if one of the following. The effective UID of the process matches the owner UID of. The calling process has the CAPFOWNER capability in its. UID of the file has a mapping. This flag is intended for use by indexing or backup programs. This flag may not be effective on all filesystems. One example is NFS, where the server maintains the access. ONOCTTY. If pathname refers to a terminal devicesee tty4it will not. ONOFOLLOW. If pathname is a symbolic link, then the open fails, with the. ELOOP. Symbolic links in earlier components of the. Note that the ELOOP error. This flag is a Free. BSD extension, which was added to Linux in. POSIX. 1 2. 00. 8. See also OPATH below. ONONBLOCK or ONDELAY. When possible, the file is opened in nonblocking mode. Neither the open nor any subsequent operations on the file. Note that this flag has no effect for regular files and block. IO operations will briefly block when. ONONBLOCK. is set. Since ONONBLOCK semantics might eventually be. For the handling of FIFOs named pipes, see also fifo7. For a discussion of the effect of ONONBLOCK in conjunction. OPATH since Linux 2. Obtain a file descriptor that can be used for two purposes to. The. file itself is not opened, and other file operations e. EBADF. The following operations can be performed on the resulting. Linux 3. 5. fstat2 since Linux 3. Linux 3. 1. 2. Duplicating the file descriptor dup2, fcntl2FDUPFD. Getting and setting file descriptor flags fcntl2FGETFD. FSETFD. Retrieving open file status flags using the fcntl2FGETFL operation the returned flags will include the bit. OPATH. Passing the file descriptor as the dirfd argument of.