Disk array is a technology that combines multiple independent disks to form a large storage system to improve data reliability, performance and capacity. There are different levels of disk arrays, and you can choose the appropriate solution according to different goals and needs. Below I will briefly introduce several common disk array levels:
- RAID 0: This is the simplest disk array level, which divides data into multiple blocks and distributes them evenly across multiple disks, called striping. This increases the speed of parallel reading and writing of data, but does not provide any redundancy or fault tolerance. If any one disk fails, the entire disk array fails and data cannot be recovered. RAID 0 is suitable for scenarios that require high performance but low reliability, such as video editing, games, etc.
- RAID 1: This is the most basic level of disk redundancy, which completely copies each data block to another disk, called mirroring. This improves data security and availability. If one disk fails, the other disk can still function normally. RAID 1 also improves read performance because data can be read from either disk. But RAID 1 also has disadvantages, it requires twice the storage space, and write performance will be affected because two disks need to be written to at the same time. RAID 1 is suitable for scenarios that require high reliability but low capacity, such as databases and logs.
- RAID 2 - This organization was inspired by the application of memory-style error correcting code (ECC) to disks. It is included because at the time of the original RAID paper, there was such a disk array product, but not since then because other RAID organizations were more attractive.
- RAID 3 - Because the high-level disk interface understands the health of the disks, it's easy to figure out which disk has failed. The designers realized that a single disk could recover from a disk failure if an additional disk contained parity for the information in the data disk. The data is organized in stripes, with N data blocks and a parity block. When a failure occurs, we just "subtract" the good data from the good blocks, and what's left is the lost data. (This is valid regardless of whether the failed disk is a data disk or a parity disk.) RAID 3 assumes that data is distributed across all disks when reading and writing, which is problematic when reading or writing large amounts of data. is attractive.
- RAID 5: This is a relatively balanced disk array level that combines striping and parity technology. It breaks the data into chunks, stripes it across multiple disks, and adds a parity block to each stripe. Parity blocks are calculated using an exclusive OR operation (XOR), which can be used to recover lost data blocks. RAID 5 can improve data read and write performance and capacity utilization, and can tolerate the failure of one disk. But RAID 5 also has disadvantages. It requires additional computational overhead to generate and update parity blocks, and if more than two disks fail, the data cannot be recovered. RAID 5 is suitable for scenarios that have certain requirements for performance and reliability, but also have limitations on capacity, such as file servers, application servers, etc.
- RAID 6: This is a disk array level that further improves reliability by adding a second parity block to RAID 5. This can improve the fault tolerance of the data and tolerate the failure of two disks. But RAID 6 also has disadvantages. It requires more computing overhead and storage space to generate and update two parity blocks, and the write performance will be lower. RAID 6 is suitable for scenarios that require very high reliability but not too high performance requirements, such as backup servers and archive servers.
- RAID 10: This is a disk array level that combines RAID 1 and RAID 0. It first divides the disks into two groups, mirrors each group for RAID 1, and then stripes the two groups for RAID 0. This can improve data performance and reliability, and can tolerate the failure of any one disk in a group of disks. But RAID 10 also has disadvantages. It requires four times the storage space, and if a disk in the same location fails in both sets of disks, the data cannot be recovered. RAID 10 is suitable for scenarios that have high requirements on performance and reliability but low capacity requirements, such as high-performance databases and high-load servers.
