Can you explain what a RAID is?

Arun Vishnu December 8, 2012
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I am seeing it so many times. What is RAID1, RAID0 etc.? Please explain it to me.

  1. Meeth Jain
    December 16, 2012 at 7:50 am

    RAID (redundant array of independent disks; originally redundant array of inexpensive disks) is a way of storing the same data in different places (thus, redundantly) on multiple hard disks. By placing data on multiple disks, I/O (input/output) operations can overlap in a balanced way, improving performance. Since multiple disks increases the mean time between failures (MTBF), storing data redundantly also increases fault tolerance.

  2. Zaphod
    December 15, 2012 at 6:17 pm - all you need to know for now ...

  3. Roomy Naqvy
    December 11, 2012 at 4:12 pm

    I don't have RAID on my PC. Usually, RAID is for servers but these days, I guess individual users would configure RAID too. RAID simply means that what you do on one hard disk gets mirrored onto another hard disk, so, in the event of any hard disk failure or any emergency, all your data is automatically backed up and safe.

  4. Samuel Mearns
    December 9, 2012 at 3:44 pm

    It has two drives one to access the most common used files (reading fast)
    one to just store some data into the drive (Writing Fast)
    When you are on a mac RAID is stored online.

  5. James Bruce
    December 9, 2012 at 11:07 am

    When you posted the question, didn't a selection of search results come up from within makeuseof? Here is the top answer which would have appeared:

  6. GamE
    December 9, 2012 at 6:02 am

    A hardware RAID controller can support several different RAID arrays simultaneously, the total number of hard drives that do not exceed the number of slots for them. In this case, the controller built into the motherboard, the BIOS settings has only two states (on or off), so the new hard disk connected with the active RAID mode unused connector on the controller can be ignored by the system until it is associated as another type of RAID array JBOD (spanned), consisting of a single disk.

    RAID 0
    RAID 0 - a disk array of two or more hard disks without redundancy (ie, essentially RAID-array is not). Data is divided into blocks of data ( A_i ) Of fixed length and is recorded on both / multiple drives simultaneously.

    (+): Due to this significantly increases the performance (of the number of disks is dependent magnification performance).

    (-): Reliability RAID 0 is definitely lower than the reliability of any of the drives separately and falls with the number of members of the RAID 0 drives, because the failure of any of the disks leads to malfunction of the array.

    RAID 1
    RAID 1 (mirroring - «mirroring") - an array of two disks that are complete copies of each other. Not to be confused with RAID 1 +0, RAID 0 +1 and RAID 10, where more than two drives, and more complex mechanisms of mirroring.

    (+): Provides an acceptable speed records and winning speed reading when parallelizing queries.

    (+): It has high reliability - works as long as the function is at least one drive in the array. The probability of a failure of two drives is the product of the probability of failure of each disk. In practice, in the event of failure of one drive should take urgent action - again a redundancy. To do this with any level of RAID (other than zero) is recommended to use disks hot spares . The advantage of this approach - to maintain high availability.

    (-): The downside is that you have to pay the cost of the two hard drives, getting useful capacity of a single hard drive.

    RAID 2
    Disks are divided into two groups for the data and error correcting codes, and if the data is stored on 2 ^ n - n - 1 disks, to store error-correcting codes to n drives. Data is striped across disks that stores information, as well as in RAID 0, ie, broken down into small units by the number of disks. The remaining disks store error correction code, which in the event of a hard disk failure is possible to recover the information. Hamming method long used in the type of memory ECC allows you to fly and fix single and two-time error detection.
    (+): increase the speed of disk compared to the performance of a single drive.
    (-):minimum number of drives in which it makes sense to use it, - 7. It should be the structure of almost double the number of disks (for n = 3, the data will be stored at 4-CD), so this kind of array not spread. If the disk is about 30-60, you get 11-19% cost overrun.

    RAID 3
    In RAID 3 array of n Disk data is broken down into pieces smaller than a sector or blocks, and distributed to n-1 drives. Another drive is used to store the parity blocks. In RAID 2 used for this purpose n-1 drive, but most of the information on the control discs used for error correction on the fly, while the majority of users satisfies the simple recovery of information in the event of failure disk, which lack the information fits on a dedicated hard disk.

    RAID 4

    RAID 4 is similar to RAID 3, but differs in the fact that the data is broken into blocks, not bytes. Thus, it was possible partly to "win" the problem of low data rate of small volume. Recording is done slowly because of the parity block is generated when writing and recorded on a single disc.

    RAID 5

    RAID5 is widespread, mainly due to its cost effectiveness. RAID5 disk array is calculated by the formula (n-1) * hddsize, where n the number of disks in the array and hddsize - the size of the smallest drive. For example, for an array of 4 drives of 80 GB total is (4 - 1) * 80 = 240 GB. To record information on the RAID 5 spent more resources and decreases performance, as it requires additional computation and write operations, but in reading has a win, because the flow of data from multiple drives in the array can be processed in parallel.

    RAID 10
    mirrored array, the data that is written sequentially across multiple disks as a RAID 0 . This architecture is an array of RAID 0, instead of individual segments which disks are RAID 1 arrays. Accordingly, the array of this level must have at least 4 disks. RAID 10 combines the high availability and performance.

    • Anonymous
      December 9, 2012 at 3:47 pm

      You forgot to mention that a RAID 5 is probably the best affordable and safe solution, very good explanation.

    • Adam Campbell
      December 9, 2012 at 10:24 pm

      This is an awesome explanation, Thanks

    • Qin Tang
      December 10, 2012 at 3:29 am

      What an answer, great!

  7. pp potana
    December 9, 2012 at 4:57 am

    It has two drives one to access the most common used files (fast)
    one to just store some data into the drive

  8. josemon maliakal
    December 9, 2012 at 3:45 am

    Redundant Array Of Independent Disks is the full form, Kind of hard disk technology ..if you wanna know more ..follow this link

  9. ha14
    December 9, 2012 at 1:20 am
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