Before introducing the important specification parameters of the disk array for everyone, the concept of the disk array is introduced firstly. The so-called Redundant Arrays of Independent Disks (RAID) has the meaning of “an array with independent disks and redundancyâ€.
The disk array is composed of a number of inexpensive disks, which are combined into a large-capacity disk group. The disk system uses the effect of the addition of data provided by the individual disks to enhance the performance of the entire disk system. With this technology, data is cut into many sections and stored on separate hard disks.
Disk array can also use the concept of parity check (Parity Check). When any hard disk in the array fails, data can still be read. When the data is reconstructed, the data is recalculated and put into the new hard disk.
Disk array important specification parameters
RAID0: RAID0 divides data in units of bits or bytes consecutively, reads/writes on multiple disks in parallel, and therefore has a high data transfer rate, but it does not have data redundancy and therefore cannot be considered a true RAID configuration. RAID0 simply improves performance and does not guarantee data reliability, and one of the disk failures will affect all data. Therefore, RAID0 cannot be used in applications where high data security is required.
RAID1: It implements data redundancy through disk data mirroring and generates mutually backed up data on paired independent disks. When raw data is busy, data can be read directly from the mirror copy, so RAID1 can improve read performance. RAID1 is the highest unit cost in disk arrays, but provides high data security and availability. When a disk fails, the system can automatically switch to mirrored disk reads and writes without reorganizing invalid data.
RAID01/10: According to the combination of RAID10 and RAID01, it is actually a combination of RAID0 and RAID1 standard, which divides data continuously in bits or bytes and reads/writes multiple disks in parallel, for each disk Make a disk image for redundancy. Its advantage is that it has the extraordinary speed of RAID0 and the high reliability of data of RAID1, but the CPU occupancy rate is also higher, and the utilization rate of the disk is relatively low. RAID1+0 mirrors and repartitions the data first, then divides all hard disks into two groups, regards RAID0 as the lowest combination, then treats these two groups as each RAID1 operation. RAID0+1 is the opposite of the RAID1+0 program. It is partitioned and then mirrored to two sets of hard disks. It divides all hard disks into two groups, becomes the lowest combination of RAID1, and treats two groups of hard disks as each RA.
ID0 operates. In terms of performance, RAID0+1 has faster read and write speeds than RAID1+0. In terms of reliability, when one RAID 1+0 disk is damaged, the remaining three disks will continue to operate. For RAID 0+1, as long as one hard disk is damaged, the other hard disk in the same group RAID 0 will also stop operating, leaving only two hard disks to operate, resulting in low reliability. Therefore, RAID10 is much more commonly used than RAID01. Most retail boards support RAID0/1/5/10, but RAID01 is not supported.
RAID2: Blocks are distributed across different hard disks, in units of bits or bytes, and use an encoding technique called “Averaging Average Error Correction Code (Hamming Code)†to provide error checking and recovery.
RAID3: It is very similar to RAID2. It is to block data distributed on different hard disks. The difference is that RAID3 uses simple parity and uses a single disk to store parity information. If one disk fails, parity disks and other data disks can regenerate data; if the parity disk fails, it does not affect data usage. RAID3 provides good transfer rates for large amounts of continuous data, but for random data, parity disks can become a bottleneck for write operations.
RAID4: RAID4 also blocks and distributes data bars on different disks, but the block units are blocks or records. RAID4 uses a disk as a parity disk. Each write operation requires access to a parity disk. At this time, the parity disk becomes the bottleneck for write operations. Therefore, RAID4 is rarely used in commercial environments.
RAID5: RAID5 does not specify parity disks individually, but instead crosses data and parity information across all disks. On RAID5, read/write pointers can operate on array devices simultaneously, providing higher data traffic. RAID5 is more suitable for small data blocks and random read-write data. The main difference between RAID3 and RAID5 is that RAID3 involves all array disks for each data transfer. For RAID5, most data transfers operate on only one disk and can operate in parallel. There is "write loss" in RAID 5, ie each write operation will generate four actual read/write operations, two of which read old data and parity information, and two write new data and parity information.
RAID6: Compared with RAID5, RAID6 adds a second independent parity block. Two independent 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 needs to allocate more disk space for parity information, and has a larger “write loss†than RAID 5, so “write performance†is very poor. Poor performance and complex implementation make RAID6 rarely used in practice.
RAID7: This is a new RAID standard. It has an intelligent real-time operating system and software tools for storage management. It can be completely independent of the host and does not occupy the host CPU resources. RAID7 can be regarded as a storage computer (Storage Computer), which is obviously different from other RAID standards. In addition to the above standards (as shown in Table 1), we can combine multiple RAID specifications like RAID0+1 to build the required RAID array. For example, RAID5+3 (RAID53) is a widely used array form. Users can generally obtain more disk storage systems that meet their requirements by flexibly configuring disk arrays.
RAID5E (RAID5Enhancement): RAID5E is an improvement based on RAID5. Similar to RAID5, data parity information is evenly distributed on each hard disk. However, some unused space is reserved on each hard disk. No striping is allowed, allowing up to two physical hard disks to fail. It seems that RAID5E and RAID5 are similar to a hot spare disk. In fact, because RAID5E distributes data on all hard disks, the performance will be better than RAID5 plus a hot spare disk. When a hard disk fails, the data on the failed hard disk is compressed to unused space on other hard disks. The logical disk maintains RAID 5 levels.
RAID5EE: Compared with RAID5E, RAID5EE data distribution is more efficient. A part of the space of each hard disk is used as a distributed hot spare disk. They are part of the array and the speed of data reconstruction when a physical hard disk in the array fails. It will be faster.
RAID50: RAID50 is a combination of RAID5 and RAID0. This configuration strips data including parity information on each disk of a RAID 5 subdisk group. Each RAID5 subdisk group requires three hard disks. RAID50 has higher fault tolerance because it allows one disk in a group to fail without causing data loss. And because the parity bit segment is on the RAID5 subdisk group, the rebuild speed is greatly improved. Advantages: Higher fault tolerance, potential for faster data read rates. It should be noted that disk failure affects throughput. The time for reconstructing information after a failure is longer than for a mirrored configuration.
The disk array is composed of a number of inexpensive disks, which are combined into a large-capacity disk group. The disk system uses the effect of the addition of data provided by the individual disks to enhance the performance of the entire disk system. With this technology, data is cut into many sections and stored on separate hard disks.
Disk array can also use the concept of parity check (Parity Check). When any hard disk in the array fails, data can still be read. When the data is reconstructed, the data is recalculated and put into the new hard disk.
Disk array important specification parameters
RAID0: RAID0 divides data in units of bits or bytes consecutively, reads/writes on multiple disks in parallel, and therefore has a high data transfer rate, but it does not have data redundancy and therefore cannot be considered a true RAID configuration. RAID0 simply improves performance and does not guarantee data reliability, and one of the disk failures will affect all data. Therefore, RAID0 cannot be used in applications where high data security is required.
RAID1: It implements data redundancy through disk data mirroring and generates mutually backed up data on paired independent disks. When raw data is busy, data can be read directly from the mirror copy, so RAID1 can improve read performance. RAID1 is the highest unit cost in disk arrays, but provides high data security and availability. When a disk fails, the system can automatically switch to mirrored disk reads and writes without reorganizing invalid data.
RAID01/10: According to the combination of RAID10 and RAID01, it is actually a combination of RAID0 and RAID1 standard, which divides data continuously in bits or bytes and reads/writes multiple disks in parallel, for each disk Make a disk image for redundancy. Its advantage is that it has the extraordinary speed of RAID0 and the high reliability of data of RAID1, but the CPU occupancy rate is also higher, and the utilization rate of the disk is relatively low. RAID1+0 mirrors and repartitions the data first, then divides all hard disks into two groups, regards RAID0 as the lowest combination, then treats these two groups as each RAID1 operation. RAID0+1 is the opposite of the RAID1+0 program. It is partitioned and then mirrored to two sets of hard disks. It divides all hard disks into two groups, becomes the lowest combination of RAID1, and treats two groups of hard disks as each RA.
ID0 operates. In terms of performance, RAID0+1 has faster read and write speeds than RAID1+0. In terms of reliability, when one RAID 1+0 disk is damaged, the remaining three disks will continue to operate. For RAID 0+1, as long as one hard disk is damaged, the other hard disk in the same group RAID 0 will also stop operating, leaving only two hard disks to operate, resulting in low reliability. Therefore, RAID10 is much more commonly used than RAID01. Most retail boards support RAID0/1/5/10, but RAID01 is not supported.
RAID2: Blocks are distributed across different hard disks, in units of bits or bytes, and use an encoding technique called “Averaging Average Error Correction Code (Hamming Code)†to provide error checking and recovery.
RAID3: It is very similar to RAID2. It is to block data distributed on different hard disks. The difference is that RAID3 uses simple parity and uses a single disk to store parity information. If one disk fails, parity disks and other data disks can regenerate data; if the parity disk fails, it does not affect data usage. RAID3 provides good transfer rates for large amounts of continuous data, but for random data, parity disks can become a bottleneck for write operations.
RAID4: RAID4 also blocks and distributes data bars on different disks, but the block units are blocks or records. RAID4 uses a disk as a parity disk. Each write operation requires access to a parity disk. At this time, the parity disk becomes the bottleneck for write operations. Therefore, RAID4 is rarely used in commercial environments.
RAID5: RAID5 does not specify parity disks individually, but instead crosses data and parity information across all disks. On RAID5, read/write pointers can operate on array devices simultaneously, providing higher data traffic. RAID5 is more suitable for small data blocks and random read-write data. The main difference between RAID3 and RAID5 is that RAID3 involves all array disks for each data transfer. For RAID5, most data transfers operate on only one disk and can operate in parallel. There is "write loss" in RAID 5, ie each write operation will generate four actual read/write operations, two of which read old data and parity information, and two write new data and parity information.
RAID6: Compared with RAID5, RAID6 adds a second independent parity block. Two independent 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 needs to allocate more disk space for parity information, and has a larger “write loss†than RAID 5, so “write performance†is very poor. Poor performance and complex implementation make RAID6 rarely used in practice.
RAID7: This is a new RAID standard. It has an intelligent real-time operating system and software tools for storage management. It can be completely independent of the host and does not occupy the host CPU resources. RAID7 can be regarded as a storage computer (Storage Computer), which is obviously different from other RAID standards. In addition to the above standards (as shown in Table 1), we can combine multiple RAID specifications like RAID0+1 to build the required RAID array. For example, RAID5+3 (RAID53) is a widely used array form. Users can generally obtain more disk storage systems that meet their requirements by flexibly configuring disk arrays.
RAID5E (RAID5Enhancement): RAID5E is an improvement based on RAID5. Similar to RAID5, data parity information is evenly distributed on each hard disk. However, some unused space is reserved on each hard disk. No striping is allowed, allowing up to two physical hard disks to fail. It seems that RAID5E and RAID5 are similar to a hot spare disk. In fact, because RAID5E distributes data on all hard disks, the performance will be better than RAID5 plus a hot spare disk. When a hard disk fails, the data on the failed hard disk is compressed to unused space on other hard disks. The logical disk maintains RAID 5 levels.
RAID5EE: Compared with RAID5E, RAID5EE data distribution is more efficient. A part of the space of each hard disk is used as a distributed hot spare disk. They are part of the array and the speed of data reconstruction when a physical hard disk in the array fails. It will be faster.
RAID50: RAID50 is a combination of RAID5 and RAID0. This configuration strips data including parity information on each disk of a RAID 5 subdisk group. Each RAID5 subdisk group requires three hard disks. RAID50 has higher fault tolerance because it allows one disk in a group to fail without causing data loss. And because the parity bit segment is on the RAID5 subdisk group, the rebuild speed is greatly improved. Advantages: Higher fault tolerance, potential for faster data read rates. It should be noted that disk failure affects throughput. The time for reconstructing information after a failure is longer than for a mirrored configuration.
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