If You Lose a Raid Can You Try Again
RAID is a technology that is used to increase the performance and/or reliability of information storage. The abbreviation stands for either Redundant Array of Contained Drives orRedundant Assortment of Inexpensive Disks, which is older and less used. A RAID organization consists of 2 or more drives working in parallel. These tin be hard discs, but there is a trend to also employ the technology for SSD (Solid Land Drives). There are different RAID levels, each optimized for a specific situation. These are non standardized by an manufacture group or standardization committee. This explains why companies sometimes come upward with their ain unique numbers and implementations. This commodity covers the post-obit RAID levels:
- RAID 0 – striping
- RAID 1 – mirroring
- RAID 5 – striping with parity
- RAID 6 – striping with double parity
- RAID ten – combining mirroring and striping
The software to perform the RAID-functionality and control the drives tin can either be located on a split up controller carte du jour (a hardware RAID controller) or it tin can simply be a driver. Some versions of Windows, such as Windows Server 2012 every bit well every bit Mac Bone X, include software RAID functionality. Hardware RAID controllers price more than pure software, but they as well offering ameliorate performance, peculiarly with RAID five and 6.
RAID-systems can be used with a number of interfaces, including SATA, SCSI, IDE, or FC (fiber channel.) There are systems that use SATA disks internally, only that have a FireWire or SCSI-interface for the host system.
Sometimes disks in a storage arrangement are defined equally JBOD, which stands for Just a Bunch Of Disks. This ways that those disks practice non use a specific RAID level and acts as stand up-alone disks. This is often done for drives that contain swap files or spooling data.
Beneath is an overview of the most popular RAID levels:
RAID level 0 – Striping
In a RAID 0 system data are split up into blocks that get written across all the drives in the array. By using multiple disks (at to the lowest degree 2) at the same fourth dimension, this offers superior I/O operation. This performance can be enhanced further by using multiple controllers, ideally 1 controller per deejay.
Advantages of RAID 0
- RAID 0 offers great performance, both in read and write operations. There is no overhead acquired by parity controls.
- All storage chapters is used, there is no overhead.
- The technology is easy to implement.
Disadvantages of RAID 0
- RAID 0 is non fault-tolerant. If one bulldoze fails, all data in the RAID 0 assortment are lost. It should not be used for mission-critical systems.
Ideal utilize
RAID 0 is ideal for not-critical storage of data that take to be read/written at a loftier speed, such as on an image retouching or video editing station.
If you want to use RAID 0 purely to combine the storage chapters of twee drives in a unmarried volume, consider mounting ane drive in the folder path of the other drive. This is supported in Linux, OS X as well equally Windows and has the advantage that a unmarried drive failure has no touch on the data of the second disk or SSD bulldoze.
RAID level 1 – Mirroring
Information are stored twice by writing them to both the information drive (or set of information drives) and a mirror drive (or set of drives). If a drive fails, the controller uses either the information bulldoze or the mirror drive for data recovery and continuous performance. You need at least 2 drives for a RAID 1 assortment.
Advantages of RAID 1
- RAID 1 offers first-class read speed and a write-speed that is comparable to that of a single bulldoze.
- In instance a drive fails, data do not accept to be rebuild, they but have to exist copied to the replacement drive.
- RAID 1 is a very uncomplicated engineering.
Disadvantages of RAID 1
- The main disadvantage is that the effective storage chapters is only one-half of the total drive capacity considering all data go written twice.
- Software RAID ane solutions do not always let a hot bandy of a failed drive. That ways the failed bulldoze can only be replaced after powering down the reckoner it is attached to. For servers that are used simultaneously by many people, this may non be acceptable. Such systems typically utilise hardware controllers that do support hot swapping.
Ideal use
RAID-1 is ideal for mission critical storage, for instance for accounting systems. It is also suitable for small-scale servers in which simply ii information drives volition be used.
RAID level 5 – Striping with parity
RAID v is the well-nigh common secure RAID level. It requires at least 3 drives but can piece of work with up to xvi. Data blocks are striped across the drives and on ane drive a parity checksum of all the cake information is written. The parity information are not written to a stock-still drive, they are spread beyond all drives, equally the cartoon beneath shows. Using the parity information, the calculator can recalculate the data of one of the other data blocks, should those information no longer be bachelor. That means a RAID 5 array can withstand a single drive failure without losing data or access to data. Although RAID 5 can be achieved in software, a hardware controller is recommended. Often extra enshroud memory is used on these controllers to improve the write performance.
Advantages of RAID 5
- Read data transactions are very fast while write information transactions are somewhat slower (due to the parity that has to be calculated).
- If a drive fails, you lot yet have admission to all data, even while the failed drive is being replaced and the storage controller rebuilds the data on the new drive.
Disadvantages of RAID five
- Drive failures have an effect on throughput, although this is still acceptable.
- This is circuitous technology. If one of the disks in an array using 4TB disks fails and is replaced, restoring the data (the rebuild time) may take a day or longer, depending on the load on the array and the speed of the controller. If another disk goes bad during that time, information are lost forever.
Ideal use
RAID 5 is a good all-circular system that combines efficient storage with excellent security and decent performance. It is ideal for file and application servers that have a limited number of data drives.
RAID level 6 – Striping with double parity
RAID 6 is like RAID v, but the parity data are written to two drives. That means it requires at least 4 drives and tin can withstand 2 drives dying simultaneously. The chances that two drives break down at exactly the same moment are of course very small. Withal, if a drive in a RAID 5 systems dies and is replaced past a new bulldoze, it takes hours or even more than a day to rebuild the swapped drive. If another drive dies during that time, you still lose all of your data. With RAID 6, the RAID assortment will fifty-fifty survive that second failure.
Advantages of RAID 6
- Like with RAID 5, read data transactions are very fast.
- If ii drives fail, you however take access to all data, even while the failed drives are being replaced. So RAID 6 is more secure than RAID 5.
Disadvantages of RAID 6
- Write data transactions are slower than RAID 5 due to the additional parity data that have to be calculated. In one report I read the write performance was 20% lower.
- Drive failures accept an result on throughput, although this is still acceptable.
- This is complex engineering science. Rebuilding an array in which one drive failed tin have a long time.
Ideal use
RAID 6 is a skilful all-round arrangement that combines efficient storage with first-class security and decent operation. It is preferable over RAID v in file and application servers that use many big drives for information storage.
RAID level 10 – combining RAID 1 & RAID 0
It is possible to combine the advantages (and disadvantages) of RAID 0 and RAID 1 in one unmarried system. This is a nested or hybrid RAID configuration. It provides security by mirroring all data on secondary drives while using striping across each prepare of drives to speed upward data transfers.
Advantages of RAID x
- If something goes wrong with 1 of the disks in a RAID 10 configuration, the rebuild time is very fast since all that is needed is copying all the information from the surviving mirror to a new drive. This can take as little as xxx minutes for drives of ane TB.
Disadvantages of RAID 10
- Half of the storage capacity goes to mirroring, then compared to large RAID 5 or RAID six arrays, this is an expensive way to accept redundancy.
What about RAID levels 2, 3, 4 and seven?
These levels practice exist simply are non that mutual (RAID 3 is essentially like RAID 5 merely with the parity information ever written to the same drive). This is simply a simple introduction to RAID-systems. You can find more than in-depth information on the pages of Wikipedia or ACNC.
RAID is no substitute for back-ups!
All RAID levels except RAID 0 offer protection from a unmarried drive failure. A RAID 6 system even survives 2 disks dying simultaneously. For complete security, y'all exercise however need to back-up the data stored on a RAID organization.
- That back-upwardly will come in handy if all drives neglect simultaneously because of a ability spike.
- It is a safeguard when the storage system gets stolen.
- Back-ups can be kept off-site at a different location. This tin come in handy if a natural disaster or fire destroys your workplace.
- The most important reason to back-up multiple generations of data is user error. If someone accidentally deletes some of import data and this goes unnoticed for several hours, days, or weeks, a good set up of dorsum-ups ensure y'all can even so call up those files.
To larn more, read the page on the all-time back-upwardly policy.
Source: https://www.prepressure.com/library/technology/raid
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