What is RAID Server, RAID Hard Drive

Mark Regan ~ November 28th, 2017 ~ Technology Overview

raid nas

Formerly, RAID was an acronym for the “redundant array of inexpensive disks”, which is now universally known as the acronym for the “redundant array of independent disks”. RAID is basically a technology for the virtualization of the storage of data which blends the components of more than one hard disk into one single logical unit mainly for performance improvement or data redundancy or both.

Redundancy

RAID, in a way, gives a method to store similar data contents at various locations on multiple physical hard disk drives (and because of this feature it is called redundant).

Note
All the RAID levels do not provide the feature of “redundancy”.

Characteristics of RAID Server

  • Performance:
    This depicts the alteration in the read speed and the write speed of whole of the array in comparison to one single disk. With the help of the placement of data on more than one disk, the (I/O) operations (input/output operations) can effectively overlap in quite a balanced way, thereby, augmenting the performance.
  • Fault-Tolerance:
    This is the capability for surviving in the circumstances of single disk failure or multiple disk failures. Now, since there are multiple disks, so it increases the MTBF, which is the mean time between failures, and thus, storing data in this redundant fashion helps in increasing the fault tolerance.
  • Capacity:
    The array capacity is usually determined through the quantity of user’s data which can be easily written to that array. The capacity of the array largely depends on which RAID level it is and it does not match always with the totting up of the RAID member disks’ sizes. For calculating the capacity of a particular RAID type along with the member disks’ set, one can make use of the free online calculator for RAID.

Levels of RAID Server, RAID Hard Drive

RAID combines many comparatively smaller and independent disks into one single storage of a much bigger size. These disks that are incorporated into the array are known as the array members. These disks can easily be united into the array in various ways called as the RAID levels.

  1. RAID 0 Level – This is basically based on the “striping”. This particular RAID level does not provide the feature of fault tolerance, whereas, it helps in augments the performance of the system (with high read as well as high write speed).
  1. RAID 1 Level – This RAID level makes use of the mirroring technique, which, in some cases, helps in increasing the read speed, and also helps in providing the feature of fault tolerance in case of the loss of not more than 1 of the member disks.
  2. RAID 0+1 Level – This RAID level is based on the blend of both, the striping as well as the mirroring technique. It inherits the performance of RAID 0 level and fault tolerance of RAID 1 level.
  3. RAID 1E Level – This RAID level makes use of both the striping as well as the mirroring technique, and can even survive the failure of 1 member disk or the failure of multiple (any number of) disks that are non-adjacent. It has 3 subtypes: 1) near, 2) interleaved, and 3) far.
  1. RAID 5 Level – This RAID level makes use of both the striping as well as the parity technique. It helps in providing an improvement in the read speed as in RAID 0 level, and also can survive the loss of 1 member disk.
  1. RAID 5E Level – This is a variation of the RAID 5 level with an only difference of the integrated additional space, which allows rebuilding of any failed array instantly in the situation of disk failure.
  1. RAID 5 Level – This has delayed parity. This RAID level is quite same as the basic RAID 5 level, but in this level, it uses the scheme of nonstandard striping.
  1. RAID 6 Level – This RAID level is quite same as the RAID 5 level, but in this, it makes use of the 2 separate parity functions. In this level too, the read speed is almost same as it is in the RAID 5 level.

Aspects in RAID Organization

There are 2 strictly independent RAID organization aspects very clearly differentiated in RAID organization. They are as follows

  1. Data organization in array using the techniques of data storage in RAID; which are:
    • Striping
    • Parity
    • Mirroring
    • Combination of the above three
  2. Specific RAID installation implementation
    • Software or
    • Hardware

Working of RAID Server, RAID Hard Drive

As we have studied before, with the RAID technology, we can mirror the data on more than 1 disk in the similar array, so that in the event of disk failure, our data is very much preserved sand safe. Thanks to this technique called as the striping technique, which is used for spreading the data over more than 1 disk drive. Then there is this option of reading/writing to multiple disks at one time, which augments the performance.

Understand; This Is Not Any Data Backup!

You should never confuse or mix RAID functionality with data backups. Even though, some of the RAID levels might provide what is known as ‘redundancy’, experts always advise to use a different storage system for the purpose of backups as well as for disaster recovery.

The Three Storage Techniques in RAID

  • Striping – Splitting data flow into blocks of specific size (known as “block size”) and after that writing of those blocks, one at a time, across the RAID. This affects only performance.
  • Mirroring – This is a storage technique which creates identical data copies stored concurrently on RAID members. This affects fault tolerance and performance too.
  • Parity – This storage technique uses striping as well as the checksum method. In this, a specific parity function is worked upon to be calculated for data blocks. In the event of any drive failure, missing blocks can be recalculated easily from checksum, providing fault tolerance.

Note

All of the accessible RAID types are all based either on striping or mirroring or parity, or o the combined application of all of the 3 storage techniques.

The RAID Implementations

RAID can be implemented in 2 ways, as follows:

  • This is done by the use of OS drivers, so it is called as the “software RAID”;
  • This is done by the use of special hardware, so it is called as the “hardware RAID”.

Hardware RAID

Hardware RAID gets formed using different hardware. Primarily, it has 2 options, as follows:

  1. Low-priced RAID chip into the motherboard,
  2. There is another option, which is a bit more expensive; it is the complex RAID controller, which is standalone, and can be easily equipped with their own cache memory with battery-back up, own CPU, and normally supporting hot-swapping.

Software RAID

This is perhaps the most economical of all RAID solutions. These days, almost every OS has a built-in power for creating RAID, even though that might not be for all the RAID levels.

Note

It must be always kept in mind that, most of the time, the software RAID will not implement hot-swapping, and therefore, you cannot use software RAID where there is a requirement of continuous availability.

Merits of Hardware RAID over Software RAID

  • It does not make use of the CPU (the Central Processing Unit) of the host machine;
  • It even allows you to form the boot partitions;
  • It also helps in handling the errors better, as it communicates directly with the devices;
  • Hot-swapping is also supported.

RAID Technology Standards

The Industry Association for Storage Networking has set up the specification of Common RAID DDF (Disk Data Format). In an attempt to support interoperability among various RAID vendors, this basically defines how the data has to be disseminated across the RAID device disks.