Redundant Array Independent Disks (RAID)
RAID or Redundant Array of Independent Disks is a technology which makes use of multiple drives or disks to maintain multiple copies of the main data for retaining the data eve in the case of data corruption due to malware or disk failure. There are many configurations in RAID which are called levels. Each level has its own configuration and advantages. Each RAID level is suitable for a specific kind of application based on the configuration of that specific level. Some of the popular levels in RAID are RAID 0 (also called Striping), RAID 1 (also called Mirroring), RAID 4 (Striping with dedicated parity drive), RAID 5 (Striping with Single Parity), RAID 6 (Striping with Dual Parity), RAID 7 (Striping with dedicated parity drive). There are also the combinations of levels like RAID 10 or RAID 1+0 (Mirroring and stripping of data), RAID 50 and RAID 60 (Combination of RAID 5 or RAID 6 with RAID 0(Mirroring)).
RAID 0 - STRIPING
RAID 0 or Stripping divides the data in the main drive into blocks and they are distributed among the drives without any redundancy. The main motive of the RAID 0 array is to enhance the r/w speeds. Also in a RAID 0 array, maximum drive space utilization would be there. All the storage in the underlying drives will be used to store data. But, RAID 0 doesn't offer any data redundancy as there is no copying of files to another drive to maintain backup or maintaining a parity of the blocks. So, RAID 0 is not suitable for critical tasks where data is to be persistent. This can be used for the applications where the performance of the disk should be high. Some of the applications where RAID 0 can be used are gaming, video editing, etc. Generally RAID 0 is used along side another copy of the same array so that this backup array can take over the RAID 0 array if the main array is damaged or corrupted. RAID 0 is generally coupled with RAID 1 which is mirroring to create combination RAID technologies like RAID 1+0 (or RAID 10) and RAID 0+1 (or RAID 01).
RAID 1 - MIRRORING
RAID 1 also called mirroring, which just copies the files to another drive (mirroring). The main application of RAID 1 is just to maintain data redundancy by compromising performance of the array. RAID 1 can withstand drive failure and retain the data from the other drive unlike RAID 0 where the whole array fails if any of the disks inside the RAID array fails. RAID 1 offers high fault tolerance which can withstand one disk failure. RAID 1 array also offers good read speeds as the data can simultaneously be read from two drives in the array. But RAID 1 is not so efficient in terms of storage utilization as only half of the total storage in the drives is usable as the other half is used to maintain the replica of the data stored. Also, there is no improvement in terms of write speeds. RAID 1 is mainly used in the critical applications like database servers in financial applications where the data integrity and fault tolerance are highly required. Also the performance of of the disks are also not compromised. The only issue with RAID 1 is that the storage is not optimal and there is no improvement in terms of write speeds
RAID 5 - STRIPING WITH SINGLE DISTRIBUTED PARITY
RAID 5 is similar to RAID 0 but RAID 5 has data redundancy unlike RAID 0. RAID 5 takes the main data strips it into chunks of data and distributes the data across the drives (same like RAID 0). The parity information of the blocks is also distributed across the drives to add fault tolerance into the RAID 0 array. So, if any drive fails, then the parity information from other drives will recover the data. This level of RAID technology doesn't compromise any aspect (either performance nor redundancy). RAID 5 utilizes almost all of the data form the drives and the performance is also balanced. RAID 5 can with stand upto one drive failure. But RAID 5 array’s write speeds are slower compared to RAID 0 and rebuilding the array after a disk failure is very time-consuming. RAID 5 is best for general applications which requires a balance between the disk performance and the redundancy.
Working of Parity in RAID
Parity bits are generated using a mathematical operation called Exclusive OR or EXOR or XOR operation. These parity bits are very useful in RAID to recover the data in case of disk failure. In RAID 5, first the block-level striping is performed on the original data. The striped data is distributed among the disks. XOR operation is performed on a set of blocks and that value is saved in the disk.
RAID 6 - STRIPING WITH DOUBLE DISTRIBUTED PARITY
RAID 6 (Striping with Double Parity) is a RAID technology similar to RAID 5 but here instead of one parity each block has double parity distributed across the drives. The additional parity enables RAID 6 to recover data even if there is a failure of 2 disks from the array. But the write speeds are even worse compared to RAID 5 and RAID 0 as the file write is associated with not one but 2 parity blocks writes. Also, RAID 5 needs a minimum of 4 drives to deploy or implement (this refuses the storage efficiency). RAID 6 is optimal for the kind of applications where the data-integrity is crucial. For example, in large scale file servers or archival storage.
There are some other RAID technologies like RAID 4 and RAID 7 which also work on the similar concept of RAID 5 and 6, but the parity blocks are stored in a dedicated parity drive and if that drive fails, there is no way the data can be recovered. Hence, those technologies are generally not used.
NESTED RAID TECHNOLOGIES
There are a number of important benefits to using RAID technologies in nested or hybrid architectures. It is feasible to customize storage solutions to meet exact performance, redundancy, and capacity needs by combining the benefits of various RAID levels. This adaptability is especially useful for maximizing storage configurations to satisfy the distinct requirements of different applications. For instance, RAID 10 (1+0) strikes a compromise between fault tolerance and performance by combining the data striping of RAID 0 with the data mirroring of RAID 1. When it comes to fault tolerance, nested RAID configurations usually outperform solo RAID levels. For example, RAID 10's dual-layered design allows it to withstand the failure of many drives, offering a strong safety net for data that is essential to the mission. This is particularly important in settings where system uptime and data integrity are critical. These integrated RAID technologies also provide performance and redundancy tweaking, which makes them a great option for environments that need a balanced strategy. RAID 50 and RAID 60 are appropriate for medium-to large-scale storage systems because they combine RAID 5 or RAID 6 with RAID 0 to provide better data safety and storage efficiency.
Another important advantage of stacked RAID is scalability. Addition drives can be easily included into the design as storage requirements increase. This scalability offers an adaptive solution for changing storage requirements when paired with the nested RAID's redundancy and optimum performance. Furthermore, when compared to more conventional RAID levels like RAID 5 or RAID 6, these configurations may result in faster rebuild times following drive failures. Rebuilding arrays can be sped up thanks to the performance and redundancy features that come with the merged levels, reducing the window of vulnerability. Because of their many uses, nested RAID technologies can be applied in a variety of contexts. They can be used to meet the complex and varied storage requirements of contemporary IT infrastructures in enterprise-class storage servers, virtualization environments, and databases.
But, it's important to think about the possible downsides. This includes things like making the setup and control of the system more complicated and needing better hardware. When deciding to use combined RAID technologies, it's important to think carefully about what you need and what you have in terms of resources, so that you can get the best outcomes. Some of the mostly used nested RAID technologies are RAID 1+0, RAID 0+1, RAID 5+0, RAID 6+0 which meet the varying requirements of various applications.
RAID 1+0
RAID 10 (RAID 1+0) is the most commonly used nested RAID technology which is a combination of both RAID 1 and RAID 0. First the data is mirrored into two drives. Then the contents of each drive are taken and a RAID array is deployed over it so that the data is stripped into 2 drives as shown in the figure below. In case of disk failure, the data can be recovered from the mirror copy of the same. RAID 10 is a dual layer approach which offers a robust combination of data redundancy and performance. RAID 10 has excellent data redundancy (due to RAID 1 - Mirroring) and high read/write speeds (due to RAID 0 - Stripping). RAID 10 also has faster rebuild speeds compared to RAID 1 as the array has to recover half of the data in case of single disk failure (as the data is stripped). But, RAID 10 is costly compared to RAID 0 and RAID 1 as the minimum required number of disks to implement RAID 10 are four. Also like RAID 1, only half of the data can be used for data storage as the other half is used for mirroring the stored data. RAID 10 can be used for the applications which require both good performance and data redundancy with fault tolerance (at most one drive from each mirrored set of disks). Some of the example use cases for RAID 10 are database servers, financial systems, storage solutions, etc. A similar kind of combination is used in RAID 01 as well (RAID 0+1). Here, first the data is stripped among two disks then the striped data is used to deploy mirroring (RAID 1) which in turn becomes a nested RAID 01. Due to stripping the performance of the array is good. RAID 01 offers high fault tolerance for the mirrored sets. Also the rebuild speeds for the array in case of disk failure in mirrored sets. But the fault tolerance offered in RAID 01 is limited as the whole stripped set is compromised if one disk is failed. Also, implementing RAID 01 is costly and is not storage efficient as well as half of the data is still used for replication.
RAID 50 and RAID 60
The main disadvantage of RAID 5 is that the write speeds are too low because of the need for writing parity blocks along with the data. And RAID 0 is very good in terms of disk performance. So, to increase the performance of RAID 5, nested RAID technology, RAID 50 came into the picture. In RAID 50, the data is initially stripped to multiple RAID 5 arrays so that we can get the fault tolerance from RAID 5 arrays and the performance boost from the RAID 0. RAID 50 array can withstand single disk failure in every RAID 5 array. Applications which require both redundancy and performance shall use this RAID technology. To implement RAID 50 the minimum number of disks required are six. RAID 50 implementation is complex as the data has to be striped to multiple RAID 5 arrays and the RAID 5 arrays has to be created prior to implementing striping. The storage efficiency is less and the requires more expenditure as we need at least of six drives to implement RAID 50. RAID 60is also similar to RAID 50. But in RAID 60, RAID 0 (Stripping) is implemented to strip the data over the RAID 6 arrays to increase the performance of RAID 6. Here, the minimum number of disks required to implement RAID 60 are eight. So, this solution is not storage efficient and is also high in cost. But, it offers high fault tolerance. RAID 60 can tolerate at most of 2 disk failures in each RAID 6 array. Also the performance is better than RAD 5 or RAID 6.