Raid concepts pdf

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Most popular in DBMS. More related articles in DBMS. We use cookies to ensure you have the best browsing experience on our website. Daniel Smith 4 drives of 3 Tb in raid 10 is 6 TB because the you combine 2 drives as raid 0 and the other 2 are used a mirror Those who work with large amounts of data should choose between raid 10 or 6 In my view today raid 5 is no longer a good solution because of bitrot..

However the most secure is in my view raid 6 till the grow beyond the max of raid 6 is reached and it looses its ability to proper restore the files. Raid10 Am I right to be scared of mirroring? Is Raid10 failure along similar lines possible? Even a software raid should be telling you which drive is malfunctioning — at least Linux will flood error log with messages of failed drive.

If you have 4 separate raid 5 arrays, would a hard drive failure in one of the arrays affect only the performance of the one array and the others would remain unaffected? Can anyone explain this? You have a file that is broken into 10 chunks, and those chunks must load into memory before you can use them. So on one dish, your hard drive controller loads block 1, then block 2, then block 3… etc. In raid 0, it would load block 1 and 2 at the same time, then block 3 and 4.

But if you lose a disk, you only have half your file. What you are recommending will not increase speeds by much, unless you are loading to files in separate folders. Thanks for beautifully explaining the types of RAID. I am a tech guy and was using RAID 5. Somehow, I had lost the data from it. So, I asked the solution from my colleague and he advised me to use Stellar Phoenix raid recovery software. This works great for me. Stellar Phoenix is a scam company and this fake comment is just sock puppet marketing.

Buyer Beware. Great post! When backing up data I always use the style strategy. But, more is always better.

You opt for Dual mirror: so in that case, no need another drive for TM? If TM, then the drive is also need 3TB? You can put other data on that partition but it apparently more common to use a separate partition. The mirrored drives protect your data against 1 disk failing. Accidental errors like incorrectly deleting a file or misplacing it or data corruption are more common and a bigger worry. That is why you use Time Machine for the data residing on the internal drive but of course the same also applies to the data that will be stored on those mirrored drives.

So in my opinion, the ideal setup is that the third drive on which you put your Time Machine data is also a 3GB drive, split into one partition for Time Machine and a second bigger partition on which you occasionally copy the main data stored on your mirrored drives. I know that adds to the cost but I like having a spare copy of data and I like having systems with disks that are all the same size.

Easier to resell afterwards, easier to repurpose as a 3-disk RAID set if your storage needs change over time. Also if I would like to use this ext for Time machine, do I need to partition as well? As have3 HD 3TB for data? I would personally opt for dual mirrored 3TB drives instead of 4x 1 TB. It is simpler, offers better performance, makes less noise and uses less power.

When you add a third disk for Time Machine you can still do it all with a 4-disk enclosure, instead of having to buy a more expensive 5-drive system. With 3 disks in use, you still hafe a spare slot if you want to expand storage in the future. If you go for a NAS box its software takes care of making those mirrored drives appear as one partition. Check out YouTube videos on setting up a Synology, Qnap,… system — it is pretty straightforward. One question. If we take RAID 5, what is pairity checksum features.

If we have 4 disk and configured raid It will do stripping means fast data flow as data being distributed but what is pairity for?

The parity is used for recovering data in case of drive failure. With RAID6 two disks can die simultaneously. More detailed descriptions of the way parity works can be found elsewhere on the web. This page is meant to give a general overview. Having an extra offsite disk is a good idea. In many NAS enclosures it is a bit of a hassle to swap drives. Once something is clunky, you stop doing it after a while. Why not use a separate harddisk docking station for the off-site copy?

I am looking to install an external multiple bay NAS drive for home use. Approximately TB, keeping in mind performance and that I will be backing up all data on an external HDD stored in my safe.

What would be the best RAID configuration to use? Thank You for any insight and information. What an excellent explanation of RAID….. Thank you so much. Hi, I have read your explanations about RAID configuration and it is very much informative with pictures. If I understand your first question correctly, you are wondering if you can use a smaller drive for parity compared to the other drives in the RAID set.

The hardware or software RAID controller determines if you can mix different sizes and types of drives. Many require all drives to have the same capacity. Alternatively they use the capacity of the smallest drive across all of them.

Please note that it is 6 gigabit per second, not 6 gigabyte per second. There is some overhead which means the fastest real transfer speed is around megabyte per second. A hard disk cannot reach that maximum speed, only SSDs are capable of doing that. You should also keep in mind that if you copy files from one logical drive to another on the same HDD, your computer is reading from and writing to the same drive simultaneously.

That also slows down the data transfer. To take advantage of Sata 3 speeds, you need both a Sata 3 drive and a Sata 3 controller. Also as noted, the 6 gigabit-per-second transfer rate specified for Sata 3 is only what the controller is capable of. A Sata 3 hard disk will never achieve a full 6Gb per second transfer rate, but it will be way faster than a Sata 2 drive.

SSDs will get you much closer than any hard drive, but no storage media will actually ever reach the maximum transfer rate of the controller. The type of data being transferred is a significant factor in this as well.

Also the 6Gb per second Sata 3 transfer rate only applies to sequential reads, which are faster than random reads, particularly on rotating media. Write operations are much slower, as the media itself is the bottleneck. Can you please tell me what is the maximum size for one virtual disk under RAID 1.

What is the largest disk size it supports? I have a Gb and a gb drives If i RAID 0 with them will I get gb of space under one drive or will it be limit to gb being to lowest size of the two? The storage space added to the array by each disk is limited to the size of the smallest one, which means this would be very unefficient. If your smallest drive is GB, then a raid 0 configuration would give you twice that amount, or GB.

You can certainly do this. I would just get a second large disk though. HDDs are moving back to being cheap again. Set aside the smaller disk for a backup drive and sync some important folders to it. The other disadvantage is that you cannot go back in time and recover a file you accidentally deleted two days ago. Previous Versions. I personally have two external disk enclosures and alternate back-ups of all data on these enclosures. One of them is stored at my parents house and during each visit I swap them out so I always have an off-site backup.

There are two disadvantages of just mirroring your data on additional internal disks: your backup is physically in the same location so if the PC gets stolen or there is a fire everything is gone. If you attach a separate box containing two or more drives to a computer and those drives are running in a RAID configuration, there is a circuit board in that box that handles the distribution of the data across the drives.

That board has its own CPU: it is effectively a mini computer but it typically is called a hardware controller. Most of it is in an alternate location 3tb and that is also spent so another external drive without a backup is being used. I am wondering if a mirrored 12 or 16 gb raid 1 drive is a good idea my current 4tb can be moved to the other locale giving me 7tb.

I anticipate using at least 1TB in the next year and possibly more. If I understand it correctly you currently have around 6 TB of data and you expect to add at least 1 TB each year.

I am not familiar with the brands you mention. Have a look at Drobo as well — their RAID boxes seem to be pretty popular but there are dozens of alternatives on the market. I would stay away from RAID with such a setup. RAID works best for drives with the same capacity and using the same type of controller. If you want higher throughput remove the big drives from their external enclosure and put them internally on SATA 6.

That is faster than most USB3 controllers. Is it possible you can explain to me how to do the following or direct me to a tutorial? On the other hand, I have lost many hard drives and all the information from crashes. Mounting drives on Windows 7 is explained on this Microsoft page. I cannot give you a short and relevant description of how to do this, especially not without any knowledge of your setup.

Once that is done, the RAID volume can be partionned and formatted from within the operating system. That depends on your definition of important. For company servers, RAID 6 is probably the way to go right now. Hi, just want to check if i understand. So for example.. A storage box consists of an array of 6 disks, 1 TB each and the effective storage capacity, based on the RAID level used is.

The way you have explained using simple terms I really liked it. But what I feel is you should have included RAID 6 as it can withstand failure of more than one disk. Its interesting to learn something that is quite different from that of others.

There are lots of heated discussions about that on the web. If you run benchmark software to measure the performance of striped SSD drives, there is a significant speed increase. Wikipedia is clearer! Fixed — Fine nuances like that are difficult to grasp for me since English is not my native language. Normal procedure is to use raid4 to resync and then revert back to raid0. From everything I am seeing on comparisons between both, if you only have 4 disks, the fault tolerance and performance are the same.

My guess based on my mathematical intuition is that if you have a number of drives that is a power of 2 it will be the same. I need to deal with very large data set with typical file size of gb, hundreds of them, in a workstation. Both read and write. Would Raid 3 be better than Raid10? Raid 5 only requires a minimum of 3 disks. As for file size, that is upto whatever file system you put on the volume created by you Raid array.

I have used RAID 6 in one of my server. Redundancy is meant to help increase the availability of your data. This means that during certain failure conditions, like when a storage drive becomes faulty, your information is still accessible and the system as a whole can continue to function until the drive is replaced. This is not meant as a backup mechanism separate backups are always recommended with RAID as with any other type of storage , but instead is intended to minimize disruptions when problems do occur.

The other benefit that RAID offers in some scenarios is in performance. With RAID, data is either redundant or distributed, meaning that multiple disks can be consulted for each read operation, increasing total throughput. Write operations can also be improved in certain configurations as each individual disk might might be asked to write only a fraction of the total data.

Some drawbacks to RAID include increased management complexity and often a reduction in available capacity. This translates to additional costs for the same amount of usable space. Further expenses might be incurred through the use of specialized hardware when the array is not managed entirely in software. Another drawback for array configurations that focus on performance without redundancy is the increased risk of total data loss.

A set of data in these scenarios is entirely reliant on more than one storage device, increasing the total risk of loss. This is known as hardware RAID.

RAID can also be configured by the operating system itself. Since the relationship of the disks to one another is defined within the operating system instead of the firmware of a hardware device, this is called software RAID. Most administrators stay away from hardware-assisted software RAID as it suffers from a combination of the pitfalls of the other two implementations.

Familiarity with some common concepts will help you understand RAID better. Below are some common terms you might come across:. The characteristics of an array are determined by the configuration and relationship of the disks, known as its RAID level.

The most common RAID levels are:. RAID 0 combines two or more devices by striping data across them. As mentioned above, striping is a technique that breaks up the data into chunks, and then alternatingly writes the chunks to each disk in the array.

The advantage of this is that since the data is distributed, the whole power of each device can be utilized for both reads and writes. The theoretical performance profile of a RAID 0 array is simply the performance of an individual disk multiplied by the number of disks real world performance will fall short of this.

Another advantage is that the usable capacity of the array is simply the combined capacity of all constituent drives. While this approach offers great performance, it has some very important drawbacks as well. Since data is split up and divided between each of the disks in the array, the failure of a single device will bring down the entire array and all data will be lost.

Unlike most other RAID levels, RAID 0 arrays cannot be rebuilt, as no subset of component devices contain enough information about the content to reconstruct the data. If you are running a RAID 0 array, backups become extremely important, as your entire data set depends equally on the reliability of each of the disks in the array. RAID 1 is a configuration which mirrors data between two or more devices.

Anything written to the array is placed on each of the devices in the group. This means that each device has a complete set of the available data, offering redundancy in case of device failure. In a RAID 1 array, data will still be accessible as long as a single device in the array is still functioning properly. The array can be rebuilt by replacing failed drives, at which point the remaining devices will be used to copy the data back to the new device. This configuration also has some penalties.

Like RAID 0, the theoretical read speed can still be calculated by multiplying the read speed of an individual disk by the number of disks. For write operations, however, theoretical maximum performance will be that of the slowest device in the array. This is due to the fact that the whole piece of data must be written to each of the disks in the array.

Furthermore, the total capacity of the array will be that of the smallest disk. So a RAID 1 array with two devices of equal size will have the usable capacity of a single disk. Adding additional disks can increase the number of redundant copies of the data, but will not increase the amount of available capacity. However, for each stripe of data written across the array, parity information, a mathematically calculated value that can be used for error correction and data reconstruction, will be written to one of the disks.

The disk that receives the calculated parity block instead of a data block will rotate with each stripe that is written. This has a few important advantages. Like other arrays with striping, read performance benefits from the ability to read from multiple disks at once.

RAID 5 arrays handle the loss of any one disk in the array. The parity blocks allow for the complete reconstruction of data if this happens.