Showing posts with label are. Show all posts
Showing posts with label are. Show all posts
Monday, November 14, 2016
RAID 2 RAID 3 RAID 4 What are the characteristics and how does it work And its history
RAID 2 RAID 3 RAID 4 What are the characteristics and how does it work And its history
RAID 2, RAID 3, RAID 4 what it is, how it works? The history lesson
After RAID 0 and RAID 1 (with RAID 1+0 and RAID 0+1) it is time for RAID 2, 3 and 4. Here we present a small description of the mentioned levels. We hope it will outline a picture of the functionality of these solutions. Although the article is a kind of history lesson these solutions are no longer used it is good to be aware of the origins of modern storage technologies.
RAID 2 the bit-level striping with dedicated Hamming-code parity
In the case of RAID 2 all data are stripped (to the bit levels not block). Each bit is written on a different drive/stripe. Such a solution requires the use of Hamming code for error correction.
Hamming code is a linear error-correcting code named after its inventor, Richard Hamming. Hamming codes can detect up to d 1 bit errors, and correct (d 1) / 2 bit errors, where d is the minimum hamming distance between all pairs in the code words; thus, reliable communication is possible when the Hamming distance between the transmitted and received bit patterns is less than or equal to d. By contrast, the simple parity code cannot correct errors, and can detect only an odd number of errors.
source
The number of discs in RAID 2 used to store information is equal to the logarithm of the number of discs that are protecting the mentioned data. All disks in RAID 2 work as one disk which has a capacity equal to the common capacity of all disks used to store data.
RAID 2
While RAID 2 is being used it is important to synchronize all disks. Such a solution requires that the controller, which makes disks, will spin at the same angular orientation in other way the index will not be reached at the same time. Disintegration will lead to total uselessness of drives in array.
Such a requirement is not the only drawback. Also the need for long Hamming code generation may prove to be problematic by slowing the whole system down.
The mode of RAID 2 action may be hard to understand. The need for using Hamming code, special controllers for disks it makes RAID 2 a not very popular solution. But if we think about it in a less pragmatic way, it may prove to be very interesting mainly due to its modus operandi. It introduces many more complex solutions than RAID 0 and RAID 1. While everything works well, RAID 2 proves to be quite a good solution in area of data security. In case of HDD failure no matter if it was the disk with data or the Hamming code any part of the array may be reconstructed by the other disks used.
While it is interesting and it has its advantages, we have not heard about any commercial implementations of RAID 2. Solutions based on it were used only in the initial phase of RAID systems usage before disks were equipped with their own correction code. Modern HDDs use various correction and optymalising algorithms. That is why the Hamming system has started to be less interesting in the area of professional usage and it is no longer implemented in modern controllers.
RAID 3 another rare one in practice
RAID 3 works as RAID 0 does it uses byte-level stripping but it also uses an additional disk in the array. It is used to store checksums and it supports a special processor in parity codes calculating so we may call it the parity disk.
RAID 3
In RAID 3, configuration data are divided into individual bytes and then saved on a disk. Parity byte is determined for each row of data and saved on the mentioned parity disk. In case of failure it allows to recover data by an appropriate calculation of the remaining bytes and parity bytes that correspond with them.
Although RAID 3 is rarely used in practice, it is worth pointing out its advantages. First of all is its resistance to damage of one disk in the arrangement. Secondly, high read speed. Unfortunately, it also has a couple of drawbacks.
The read speed is more than satisfactory but write speed is on the contrary the reason being the necessity of checksums calculating (even RAID hardware controllers cannot solve this problem). She second disadvantage is a matter of disk failure. When it happens, the whole system will work much slower. What is more, although RAID 3 is resistant to breakdown (in case of failure of one disk in the array), replacing a damaged disk is very costly. A third problem is the disk used for calculating checksums it is usually the bottleneck in the performance of the entire array.
As can be easily seen, RAID 3 is not a good, reliable or cheap solution. Therefore, as it was mentioned earlier, its use is rare in practice. Systems based on RAID 3 are mostly purposed for implementations where a small number of users refer to the very large files.
RAID 4 smells like RAID 3 and 5
RAID 4 is very similar to RAID 3. The main difference is the way of sharing data. They are divided in to blocks (16, 32, 64 lub 128 kB) and written on disk s similar to RAID 0. For each row of written data, any recorded block is written on a parity disk. In short this means that RAID 4 does not strip data at block levels but it uses byte levels for striping (block-level striping with a dedicated parity disk).
There are also similarities in relation to RAID 5, but it confines all parity data to a single drive. RAID 4 does not use distributed parity.
RAID 4
RAID 4 requires at least three disks for complete implementation and configuration. What is more, it also needs hardware support for parity calculations. This makes it possible to recover data by the appropriate mathematical operations.
If we asked: what is RAID 4 for? we would point out one particular need. Such a solution will work very well in the case of really large files when sequential read and write data process is used. Using RAID 4 for small portions of data would be not a good idea. The reason is the need to carry out modifications of parity blocks for each I/O session. The need for continuous repeating of such an operation would cause large losses of time and slow down a whole system.
RAID 3 and RAID 4 solutions were replaced by RAID 5. You can read about it in an article by Janusz B?k: How does RAID 5 work? The Shortest and Easiest explanation ever!
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Monday, September 19, 2016
What are the hidden costs
What are the hidden costs
What are the hidden costs?
RAID recovery is not finished when parameters are detected. Once the parameters are detected you have to either
- write a copy of the RAID somewhere if all RAIDs content is needed
- use regular data recovery program if only some files are needed.
If you have enough unused hard disks or a license of any data recovery program compatible with ReclaiMe Free RAID Recovery, then no hidden costs are involved. If neither of these is available, you will have to pay for either a storage, or a data recovery software.
Our RAID Recovery software works with
- hard drives (internal and external),
- disk image files,
- disks from hardware and software RAIDs,
- disks from most all NAS devices.
Note: ReclaiMe Free RAID Recovery software needs Windows to run. It does not run on Apple Mac or Linux environment.
Difference between ReclaiMe File Recovery and ReclaiMe Free RAID Recovery
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Monday, September 5, 2016
Psychological Problems Be Careful When You are going to be grown as a Freelancer
Psychological Problems Be Careful When You are going to be grown as a Freelancer
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Thursday, August 18, 2016
What are the Weakness of Windows 8 1
What are the Weakness of Windows 8 1
What are the Weakness of Windows 8.1
What are the Weakness of Windows 8.1 - Project Zero is a Google activity that targets shortcomings in distinctive programmings that are at present accessible in the business sector, in the wake of deciding the conceivable helplessness of those projects it is then appeared for its individual merchant for them to have the capacity to fix it before programmers can utilize those vulnerabilities to endeavor their frameworks. On the other hand, Google just gives the engineer a 90-day restrain keeping in mind the end goal to make a patch to alter the issue and after that Google will distribute the escape clause alongside codes that could misuse it. Tragically for Microsoft the 90-day window has effectively terminated and the tech goliath has yet to create a patch for the located issues on its product.
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| What are the Weakness of Windows 8.1 |
A scientist taking a shot at the Windows 8.1 figured out that a vast security opening is open for programmers to endeavor. The helplessness will permit low-level clients, for example, Guests to get to and pick up Administrator rights, consequently providing for them full control and access to touchy and potentially harming capacities. After Google Zero group educated Microsoft of the conceivable security shortcoming in their framework, Microsoft was given precisely 90 days to make a patch to settle it. Tragically for Microsoft, no patch was made and Google distributed the security defect days back, right on timetable.
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| windows 8.1 |
A few masters say that Google is accomplishing more damage than great with its Project Zero, particularly calling attention to the adaptability of its distributed due date. The individuals who are on Googles side say that the 90-day window is reasonable and sensible enough for any designer or merchant to make a patch for their products own particular shortcomings. Others are guiding fingers toward Microsoft for their absence of consideration concerning their own particular security provisos. In this way, no hacks were accounted for to have utilized the found escape clause and as per Microsofts official explanation with respect to the matter, they are right now "attempting to discharge a security redesign to address an Elevation of Privilege issue."
What are the Weakness of Windows 8.1
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