Teach you to install the disk array: Build RAID requires several hard drives _ server other

There are two ways that a disk array can be implemented, that is, "software arrays" and "hardware arrays."

A software array is the Disk management function provided by the network operating system itself to configure multiple hard disks on a connected common SCSI card into a logical disk to form an array. The software array can provide data redundancy, but the performance of the disk subsystem will be reduced, some of the reduction is still relatively large, up to 30%.
The hardware array is implemented using a dedicated disk array card. The hardware array can provide online capacity, dynamically modify array level, automatic data recovery, drive roaming, super high-speed buffering and other functions. It provides solutions for performance, data protection, reliability, availability, and manageability. Array card-specific processing unit, which performs much better than conventional non-array hard drives and is more secure and stable.

for home users is the solid-state drive to do the system disk, and then use two pieces of the same mechanical hard disk to do high-speed RAID 0, if there is data security requirements, you can consider raid 0+1, a four-disk raid 0+1 as an example, the data storage mode as shown in the figure: RAID 0+ 1 is a balanced solution for both storage performance and data security. It provides the same data security as RAID 1, and provides similar storage performance to RAID 0.

RAID technology mainly includes several specifications, such as RAID 0~raid 7, which have different emphases, and the common specifications are as follows ( The following illustration also shows the minimum number of disks required for each RAID ):
RAID 0:raid 0 splits data in bits or bytes sequentially, reads/writes on multiple disks in parallel, and therefore has a high data transfer rate, but it does not have data redundancy and is therefore not a real RAID structure. RAID 0 simply improves performance and does not guarantee data reliability, and one of the disk failures affects all data. Therefore, RAID 0 cannot be applied to situations where data security requirements are high.

RAID 1: It is data redundancy through disk data mirroring, generating data that is backed up on a pair of independent disks. When raw data is busy, the data can be read directly from the mirrored copy, so RAID 1 can improve read performance. RAID 1 is the highest unit cost in a disk array, but provides a high level of data security and availability. When a disk fails, the system can automatically switch to read and write on the mirrored disk without the need to reorganize the failed data.

RAID 0+1: Also known as the raid 10 standard, is actually a combination of RAID 0 and RAID 1 standards, in which the data is continuously split in bits or bytes and read/write in parallel, while disk mirroring for each disk is redundant. The advantage of this is that it has a high speed of RAID 0 and reliable data for RAID 1, but CPU usage is also higher and disk utilization is low.

RAID 2: The data is fragmented across different hard disks, in bits or bytes, and is used to provide error checking and recovery using a coding technique called "aggravating average error correction codes (SEA code)". This coding technique requires multiple disk storage checking and recovery information, making RAID 2 technology more complex to implement and therefore rarely used in a business environment.

RAID 3: It is very similar to Raid 2, where the data is striped across different hard disks, except that RAID 3 uses simple parity and a single block of disk to store parity information. If a disk fails, the parity disk and other data disks can be reused, and if the parity disk fails, the data is not used. RAID 3 provides a good rate of transmission for a large number of contiguous data, but for random data, a parity disk can be a bottleneck for write operations.

RAID 4:raid 4 also bars data and distributes it across different disks, but the bar units are blocks or records. RAID 4 uses a disk as a parity disk, each write operation requires access to the parity disk, then the parity disk will become the bottleneck of the write operation, so raid 4 in the business environment is also rarely used.

RAID 5:raid 5 does not specify parity disks separately, but instead accesses data and parity information across all disks. On RAID 5, the read/write pointer can operate on the array device at the same time, providing higher data traffic. RAID 5 is more suitable for small blocks and randomly read and write data. The main difference between RAID 3 and RAID 5 is that RAID 3 involves all the array disks for each data transfer, while for RAID 5, most data transfers are done on a single disk and can be done in parallel. There is "write loss" in RAID 5, that is, each write will produce four actual read/write operations, of which two read old data and parity information, two times to write new data and parity information.

RAID 6: RAID 6 increases the second independent parity information block compared to RAID 5. Two separate parity systems use different algorithms, the reliability of the data is very high, even if two disks fail at the same time will not affect the use of data. However, RAID 6 requires more disk space to be allocated to parity information and has a much greater "write loss" than RAID 5, so "write performance" is very poor. Poor performance and complex implementations make RAID 6 less practical.

RAID 7: This is a new RAID standard with its own intelligent real-time operating system and software tools for storage management that can be completely independent of the host's CPU resources. RAID 7 can be viewed as a storage computer (Storage Computer), which is significantly different from other RAID standards. In addition to the above criteria (table 1), we can combine a variety of RAID specifications, such as RAID 0+1, to build the desired RAID array, such as RAID 5+3 (RAID 53), which is a more widely used array form. Users can generally gain a disk storage system that is more responsive to their requirements by flexibly configuring the disk array.

RAID 5E (RAID 5 enhencement): Raid 5E is an improvement over RAID 5 levels, similar to RAID 5, where data is evenly distributed across hard disks, but a portion of unused space is retained on each hard drive, which is not striped. Up to two physical hard drives are allowed to fail. It looks like the raid 5E and RAID 5 plus a hot spare are similar, but because RAID 5E distributes data across all the hard drives, performance is better than a RAID5 plus a hot spare. When a hard drive fails, the data on the failed hard drive is compressed to unused space on the other hard drive, and the logical disk remains at the RAID 5 level.

RAID 5EE: RAID 5EE data distribution is more efficient than raid 5E, part of each hard disk is used as a distributed hot spare, they are part of the array, and data is rebuilt faster when a physical hard disk fails in the array.

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RAID 50:RAID50 is a combination of RAID5 and RAID0. This configuration splits data, including parity information, on each disk of the RAID5 's sub-disk group. Each RAID5 Sub Disk group requires three hard drives. RAID50 has a higher fault tolerance because it allows one disk in a group to fail without causing data loss. And because the odd-even bit is in the RAID5 sub-disk group, the reconstruction speed is greatly improved. Advantages: Higher fault tolerance, with the potential for faster data reading rates. It should be noted that disk failure can affect throughput. The time to reconstruct information after a failure is longer than the mirrored configuration.