Redundant Array

DVS Archiving and Storage

Anthony C. Caputo , in Digital Video Surveillance and Security (2d Edition), 2014

Redundant Array of Contained Disks (RAID)

A RAID is a method of combining two or more hard drives in a format that enhances reliability or operation. At that place are many types of RAID, but RAID 0 (goose egg) and RAID 5 arrays (see Figure 9.13) are most popular because they tin can "stripe" data across multiple drives for maximum performance. When you're upgrading, consider purchasing a figurer with built-in RAID functionality (usually listed as a characteristic of the motherboard), which allows you to use RAID formatting from at least a pair of identical hard drives. Although many systems use RAID 0 arrays, they are very risky. If one of the drives in a RAID 0 array fails, they all fail. See Table 9.three for a listing of bachelor RAID levels.

FIGURE nine.thirteen. RAID array.

Table 9.3. RAID Formatting Variations

Level Description Minimum No. of Difficult Drives
RAID 0 RAID 0 offers improved performance through striping data over multiple hard drives. By doing this, storage capacity is increased, but in that location is no back-up or fault tolerance. When a unmarried difficult drive fails, information technology destroys the entire array. ii
RAID i By adding a mirroring function, RAID 1 provided mistake tolerance from deejay failure of all but 1 of the drives in the array. There is also an increase in read performance when a multithreaded operating system (seeking two places and the same time) is used. 2
RAID ii Using what is chosen hamming code parity, the disks in the array are synchronized and striped in unmarried bytes and/or words. 3
RAID three RAID 3 offers fault tolerance similar to RAID v, but considering the byte-level strip is smaller than a file system block, the read and write to the assortment act as a single bulldoze. All the drives must have synchronized rotation for this to work properly, just if 1 difficult drive fails, the operation doesn't change. 3
RAID 4 Similar to RAID 3 but uses cake-level instead of byte-level striping. Data files tin can be distributed across multiple disks, so as each disk operates independently, this allows for parallel I/O requests, reducing information transfer speeds only offering error detection through dedicated parity on a separate, single difficult drive. 3
RAID 5 The major do good of RAID 5 is that the distributed parity requires all drives only ane to be nowadays to operate, and then if there is a single difficult drive failure, the array is not destroyed. Using a distributed parity, upon a difficult drive failure reads are recalculated and the end user is unaware of a hard bulldoze loss. However, if a second drive inside the array fails, there can be data loss, and the whole assortment is vulnerable and will have reduced performance until the hard drive is replaced and the information on the failed drive is restored. 3
RAID vi Similar to RAID 5 but fault tolerance includes the power to go on to function, even with two failed difficult drives in a single array. As with RAID 5, the whole array is vulnerable and will have reduced performance until the difficult drives are replaced and the data on the failed drive is restored. The larger the hard drive capacity, the longer the restoration of the difficult drives volition take. Dual parity adds extra fourth dimension to the array restoration, without the information being at adventure if another boosted hard drive fails before the complete restoration of the previous failed hard drives. 4

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Installing Linux

Graham Speake , in Eleventh Hour Linux+, 2010

RAID

RAID uses your disk subsystem to provide enhanced read/write performance, protection against data lost due to deejay failures, or both. It can be implemented using hardware specific RAID controllers (Hardware RAID) or functionality embedded inside the operating system (Software RAID).

Did You Know?

RAID subsystems require two or more disks to form one virtual disk. The differences between software and hardware RAID solutions are every bit follows:

■

Hardware-based RAID performs faster than the software-based RAID implementation because software-based RAID requires more CPU time and has additional retentiveness requirements.

■

Software-based RAID is operating system dependent and hardware-based RAID is vendor independent.

■

Hardware-based RAID may be more expensive than software-based RAID as it may require additional hardware components (for example, RAID controllers), unless incorporated on your motherboard.

RAID technology requires an understanding of three bones concepts: striping, mirroring, and parity. Striping joins the hard disk drive drives together to form i big deejay drive. For example, three 300 MB drives joined together in a striping array will class a single 900 MB drive. Striping evenly writes data beyond all of the disks independent in the array and will evenly read data from all disks contained in the array, increasing overall disk subsystem performance. The downside to striping is that it does non provide any fault tolerance.

Mirroring forms 1 disk drive whose size is adamant by the size of the smallest drive, and the same information is written to both drives, providing a level of redundancy in the result i bulldoze crashes. The disadvantage of mirroring is the impact of having to record the same information twice across two different drives which reduces the disk subsystem performance. Parity stores information in the disk assortment subsystem that can exist used to rebuild files or lost data in the event 1 of the disks in the disk subsystem array fails. Dissimilar striping and mirroring, parity requires a minimum of three disks inside the deejay assortment subsystem. Each of these techniques is assigned a different RAID level.

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Video Management Systems

Vlado Damjanovski , in CCTV (Third Edition), 2014

RAID-6

RAID-vi (block-level striping with double distributed parity) provides fault tolerance up to 2 failed drives. This makes larger RAID groups more practical, especially for high-availability systems. This becomes increasingly important as large-chapters drives lengthen the time needed to recover from the failure of a single drive. Like RAID-five, a single drive failure results in reduced functioning of the entire assortment until the failed bulldoze has been replaced and the associated data rebuilt. This RAID is also used in some CCTV recorders.

RAID-vi (2 drives tin can neglect)

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Mass Storage

Thomas Sterling , ... Maciej Brodowicz , in High Performance Computing, 2018

Aggregated Storage534

17.iv.1

Redundant Array of Contained Disks 534

17.four.1.ane

RAID 0: Striping534

17.4.1.2

RAID 1: Mirroring535

17.iv.one.3

RAID 2: Bit-Level Striping With Hamming Lawmaking536

17.4.ane.4

RAID 3: Byte-Level Striping With Dedicated Parity536

17.4.1.5

RAID 4: Block-Level Striping With Dedicated Parity537

17.four.1.6

RAID 5: Block-Level Striping With Unmarried Distributed Parity538

17.four.1.7

RAID six: Block-Level Striping With Dual Distributed Parity539

17.iv.one.8

Hybrid RAID Variants539

17.4.two

Storage Surface area Networks541

17.4.3

Network Fastened Storage543

17.iv.4

3rd Storage544

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Locking Down Your XenApp Server

Tariq Bin Azad , in Securing Citrix Presentation Server in the Enterprise, 2008

RAID 5

RAID 5 is disk striping with parity. With this level of RAID, data is striped across three or more than disks, with parity information stored beyond multiple disks. Parity is a calculated value that'southward used to restore data from the other drives if one of the drives in the set fails. It determines the number of odd and even bits in a number, and this data is used to reconstruct data if a sequence of numbers is lost, which is the instance if one of the disks fail.

Because RAID 5 requires parity information to be calculated, the functioning of your server can decrease when information is written using this level of RAID. However, performance tin can increase when information is read, considering the data is read from multiple disks at once. Since there tin can be upwardly to 32 disks making up RAID 5 array, this can be a significant reward. However, when a disk fails, the performance decreases because the server must reconstruct the data from parity data on the other disks.

RAID v also offers better deejay utilization than RAID i.When you mirror a disk, yous must buy twice the amount of disk space that yous'll actually use for data. L percentage of the full deejay space is used for redundancy. With RAID 5, the amount of space used for parity is equal to ane disk in the array, so the more disks yous employ, the college your pct of deejay utilization. For example, if you have 10 disks in the array, only i-10th of the total disk infinite is used for back-up and 9-tenths of the infinite is available for data.

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Operation Tuning

Kelly C. Bourne , in Application Administrators Handbook, 2014

17.5.1.three.3 RAID

RAID (Redundant Array of Independent Devices) arrays use software to combine numerous drives together to make them appear as a single device. There are several levels of RAID that emphasize increasing operation, enhancing redundancy, or both.

Implementing a RAID assortment for your application isn't without certain drawbacks. Some potential downsides of implementing a RAID array are:

•

Information technology's some other layer of complexity that needs to exist managed. If neither you lot nor your organization has experience with RAID arrays, and so this is an boosted expanse of expertise that needs to exist acquired.

•

It isn't free. In that location is a toll to the boosted disk drives and the software that manages a RAID subsystem. Be certain that the benefits outweigh the costs for your installation.

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Information Redundancy

Israel Koren , C. Mani Krishna , in Fault-Tolerant Systems (2d Edition), 2021

3.ii.6 Hierarchical RAID

RAID structures can be organized hierarchically. Before explaining this organization, we innovate one level of RAID that does not include whatever redundancy: RAID level 0.

Level 0 is an system, where the information are interleaved between ii disks. There is no parity scrap or other class of redundancy here, but parallelism. (In that sense the term RAID is misapplied here: the array of disks contains no redundancy.) The purpose is to increase data throughput to and from the disks past assuasive parallel accesses.

Let usa now consider hierarchical arrangement. The nomenclature for the level is Level ij, Level i/j or Level i+j, cogent that the disks consist of a RAID Level j organization of units, where each unit is organized as a RAID Level i entity.

Example: RAID level 50 (see Fig. 3.26) consists of a RAID level 0 arrangement of units, each unit consisting of a RAID level 5 structure. So, given a file consisting of segments 0 , 1 , ii , 3 , ⋯ , we would assign segments 0 , 2 , 4 , ⋯ to exist stored in i group of disks, whereas 1 , 3 , 5 , ⋯ would be stored in the other. Each of these two groups is organized as a RAID Level 5 construction.

Figure 3.26

Effigy 3.26. RAID50 structure.

Similarly, RAID31 consists of a RAID level 1 organisation of units, each unit consisting of a Level 3 structure. The Level ane organisation is mirroring, so Level 31 consists of two mirrored RAID level three entities, i.east., two Level iii entities, which are copies of each other. Each of these organizations has its ain distinctive characteristics.

Example: Annotation that the striping is not directly "visible" from outside the RAID grouping. Thus for example, if a file is striped within a RAID group, the private stripes are not separately accessible from outside. This makes a difference in the speed with which recovery can exist effected.

To see why, permit usa compare RAID10 and RAID01. Suppose each of these arrangements contains six disks in all. In RAID10 (Fig. 3.27), these six disks would be organized into iii groups of mirrored disks (RAID 0 at the lower level; RAID 1 above). In RAID01 (Fig. 3.28), nosotros would accept two groups at the higher level mirroring each other; each of these groups consisting of three disks.

Figure 3.27

Figure 3.27. RAID10 construction.

Figure 3.28

Figure 3.28. RAID01 structure.

Suppose Disk 0 fails in RAID01. The lower-level controller cannot, by itself, fix the problem, since it does not accept whatever redundant data within its reach. It has, instead, to obtain the data from the controller of the other low-level group.

By contrast, suppose Disk 0 fails in the RAID10 configuration. The lower-level controller in charge of that disk tin can resolve the trouble by itself: when a new disk is inducted into the system, this controller simply copies its (good) disk, i.eastward., Disk i, into the new 1. The volume of data copied is therefore much less in RAID10 than for RAID01. This translates into a quicker recovery from failure; annotation that the system is vulnerable to a 2d failure while it is however recovering from the first. As disk sizes increase and the recovery time increases, this difference may be significant.

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Cyber Forensics

Scott R. Ellis , in Computer and Data Security Handbook (Third Edition), 2013

Redundant Array of Independent (or Inexpensive) Disks

Acquiring an entire redundant array of independent (or inexpensive) disks (RAID) set up disk by disk and then reassembling them in EnCase is probably the easiest fashion to deal with a RAID and may be the only way to capture a software RAID. Hardware RAIDs tin exist almost efficiently captured using a boot disk. This allows the capture of a single volume that contains all unique data in an array. It can be trickier to configure, and every bit with everything, practice makes perfect. Be sure yous empathize how it works. The worst thing that can happen is that the incorrect deejay or an unreadable disk gets imaged and the job has to be redone at your expense.

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Installing and configuring Windows Server 2008 R2

Dustin Hannifin , ... Joey Alpern , in Microsoft Windows Server 2008 R2, 2010

Creating a RAID five volume

The procedure of creating a RAID-5 volume is very similar to creating a mirrored volume. This time you will demand to ensure that you take at least 3 disk drives to be included in the RAID array. One time the drives are installed, you are ready to create the RAID-5 volume.

1.

Log on to the server, open Server Manager, and expand Disk Management.

2.

You may demand to bring the newly installed drives online by right clicking on each drive and choosing the online option.

3.

Once the disk drives are online, they tin be initialized by right clicking on each drive and choosing Initialize.

iv.

You can now institute a new RAID-5 volume by correct clicking on the get-go bulldoze to exist used in the array and choosing New RAID-v volume as seen in Figure two.xix.

Figure ii.19. Create new RAID-five Volume.
5.

The New RAID-v Volume Sorcerer will launch. Click Side by side to brainstorm.

half dozen.

Add together the drives you lot desire to include in the RAID-5 book, using the Select Disks page (see Figure ii.20). Recall that you lot will demand to include iii or more than disk drives to create a RAID-5 volume. After you have selected the deejay drives to use, click on the Next button to go along.

Figure 2.20. RAID-5 Book Drive Selection.
7.

Select a bulldoze letter to be used and click Next.

8.

Choose the selection to Perform a Quick Format and optionally give the new volume a meaningful label and then click Next.

9.

At the summary page of the wizard, verify the settings you have selected, and then click on the End button to create the RAID-5 volume.

x.

Y'all will exist prompted to catechumen the drives to dynamic. Click Yeah to convert the disks to dynamic.

11.

You take now established a newly formatted RAID-5 book as seen in Figure 2.21.

Effigy 2.21. Newly Created RAID-five Book.

Notes from the field

Shrinking volumes

Starting with Windows Server 2008 R1, y'all can shrink volumes to a smaller size if you need to do and then. To shrink a volume, right click on the book and choose shrink. Y'all volition exist asked to enter the new size, and the volume will exist shrunk to that size.

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Information communications technology

Paul S. Ganney , in Clinical Engineering (Second Edition), 2020

Resilience using RAID

Probably the about common type of resilience, especially on a server, is Redundant Array of Contained Discs (RAIDs). 26 At that place are several forms of RAID and we consider two (levels one and v) here. RAID level 1 is a simple disc image, equally per replication above – merely in existent-fourth dimension. The replication is handled by the RAID controller (a disc controller with additional functionality) which writes any data to both discs simultaneously. If one disc fails, so the other can exist used to go along the arrangement operational. The failed disc may and then be replaced (often without halting the organization – known every bit "hot swapping") and the RAID controller builds the new disc into a copy of the electric current primary over a catamenia of time, depending on the corporeality of information held and the processing load.

Other forms of RAID do not replicate the data directly, merely spread information technology across several discs instead, adding in some error correction every bit well. The class of spreading (known as "striping") and the type of error correction are different for each level of RAID.

RAID 5 uses cake-level striping and parity data, spread across all discs in the array. In all disc storage, the disc is divided up into a set of blocks, a cake existence the smallest unit of addressable storage. A file will therefore occupy at to the lowest degree i block, even if the file itself is only one byte in size. A read or write performance on a disc volition thus read or write a fix of blocks. In RAID five these blocks are spread across several discs, with parity information stored on another ane (see Fig. eight.2). Thus RAID 5 always requires a minimum of 3 discs to implement.

Fig. 8.2. Diagram of a RAID 5 setup. xxxii Each letter represents the group of blocks in the respective parity block (a stripe).

Parity, which we met in "encryption", is a informatics technique for reducing information corruption. Information technology was originally designed for data transmission and consisted of adding an extra bit to the data. 27 This extra scrap forced the sum of the bits to be odd (odd parity) or fifty-fifty (even parity). It was added at manual and checked at reception (although this would only detect i fault). 28 More complex forms used more than bits which enabled the data not just to be amend checked, but also to be corrected. Such codes are known as Hamming codes. 29 The parity used within RAID 5 not simply checks that the data is correct, only enables it to exist re-congenital, should a disc fail and have to be replaced. xxx A RAID controller is also able to recreate the missing data in real fourth dimension, resulting in minimal deposition of service.

In the figure, the distribution of the blocks and the parity tin can conspicuously be seen. Distributing the parity blocks distributes the load across all the discs, as this is where bottlenecks may appear (to read blocks B3 to C1, for instance, also requires two parity blocks to be read – in this case each disc merely has 1 read operation to perform). RAID 5 has found favour as information technology is viewed as the best cost-effective option providing both good performance and good back-up. As write operations tin can be wearisome, RAID 5 is a good choice for a database that is heavily read-oriented, such every bit paradigm review or clinical wait-up.

As has been mentioned, a RAID controller can keep a system operational even when a disc has failed, so much and so that users may not notice. It is therefore imperative to monitor such clusters as one failure may exist easily stock-still just two may be catastrophic.

Traditionally calculator systems and servers have stored operating systems and data on their own dedicated disc drives. With the information requirements expanding it has now become more common to take separate large data stores using NAS or SAN technology. These differ in their network connectivity but both rely on RAID for resilience. NAS uses TCP/IP connections and SANs use Fibre Channel connections.

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