RAID, short for Redundant Arrays of Independent Disks, Chinese for cheap redundant disk arrays. In 1987 by the U.S. Berkeley proposed

RAID (Redundant Array of Inexpensive Disks) theory, as a high-performance storage system, has been more and more widely used. RAID level

From the concept of RAID to the present, has developed a number of levels, there are clear The standard levels are 0, 1, 2, 3, 4, 5 and so on. But the most commonly used are 0, 1, 3, 5 four

levels. Others are 6, 7, 10, 30, 50, etc. RAID reduces costs for users, increases execution efficiency, and provides stability in system operation.

RAID Disk Array is a simple explanation of how multiple hard disks can be combined into a single virtualized high-capacity hard

disk drive through the RAID Controller (Hardware, Software), featuring multiple hard disks that can be read simultaneously at higher speeds and providing fault tolerance.

The main access to Dat

a storage is not a Backup Solution.

There is a basic concept in RAID arrays called EDAP (Extended Data Availability and Protection), which emphasizes expandability and fault tolerance mechanisms

This is the first time that RAID arrays have been used in the market.


Data Ready
Data Ready is a video ready to be used as a standalone application for the latest generation of DiskStation? HDDs.

RAID disk arrays support rebuilding of hard drive failures.

RAID Disk Arrays support Hot Spare without the need for downtime.

RAID Disk Arrays support Hot Swap without the need for downtime.

RAID Disk Arrays support expanding hard drive capacity and more.

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RAID array level

NRAID:

NRAID:

The hard disks are used continuously.NRAID means that the RAID function is not used. It uses the total capacity of the hard disks to form logical disks (no stripe reads or writes are used). In other words, it

generates the logical disk capacity as the sum of the physical disk capacity. In addition, NRAID does not provide data redundancy.

JBOD:

JBOD means that the controller treats each hard disk in the machine as a separate drive, so that each drive is used as a single independent logical disk.

In addition, JBOD does not provide data redundancy.

RAID0: RAID0 - Disk Stripping without parity (commonly used)

Also known as data chunking, this is the process of dividing data into equal-sized chunks and writing them to different hard disks on the array, a technique also known as "stripping. "

(i.e., data striping), which distributes data across multiple disks and operates each disk in parallel when reading and writing. Theoretically, its capacity and

data transfer rate is N times that of a single hard disk. n is the total number of hard disks that make up RAID0. N is the total number of hard disks in the RAID0 configuration. Of course, if the array controller has multiple hard disk channels, the I/O performance will be higher if the hard disks on the multiple channels are operated in a RAID0 configuration. Therefore, it is commonly used in the field of graphics, video, etc. RAID0 I/O transfer rate is higher, but the mean time to failure MTTF is only Nth of that of a single disk

one, so RAID0 reliability is the worst.

RAID1: RAID 1 - Disk Mirroring (more commonly used)

Also known as mirroring. That is, each working disk has a mirror disk, each time you write data must be written to the mirror disk at the same time, read data only from the working disk read out, once the working disk

failure to immediately transfer to the mirror disk, read data from the mirror disk. When replacing the faulty disk, the data can be reconstructed to restore the correct data to the working disk, this array is very

high reliability, but its effective capacity is reduced to less than half of the total capacity, so RAID1 is commonly used in the application of very strict requirements for fault tolerance, such as finance, finance and other fields.

RAID (0+1):

Combines RAID 0 and RAID 1 - striping reads and writes while using mirroring operations. RAID (0+1) allows multiple hard drives to be damaged because it uses the hard drives exclusively

for data redundancy. RAID (0+1) is automatically implemented if there are more than two hard disks doing RAID 1.

RAID 2:

Also known as bit-crossover, it uses Hamming code for disk error checksums and bit-crossover access for large data reads and writes, but the redundancy overhead is too high (more than one checksum disk), and has been eliminated.

RAID3: RAID 3 - Parallel Disk Array

For single-disk fault-tolerant parallel transmission. That is, it uses Stripping technology to chunk the data, performs heterodyne checksums on these chunks, and the checksum data is written to the last hard disk. It

is characterized by a disk for the checksum disk, data stored in bits or bytes in each disk (scattered records in the group of the same sector of each hard disk). When a hard disk fails

When a hard disk fails, the write operation continues to operate on the data and checksum disks, except for the failed disk. Read operations are performed by reconstructing the data that should be on the failed disk through heterodyne calculations on the remaining data and parity disks

The advantages of RAID3 are parallel I/O transfers and single-disk fault tolerance, which provides a high level of reliability. Disadvantages: each read or write has to involve the entire group, and only one I/O can be completed

at a time.

RAID4:

Similar to RAID3, with the difference that RAID3 is cross accessed on a bit- or byte-by-bit basis, while RAID4 is accessed on a block- by-block basis (sector by sector), and can be operated individually on a particular disk

No need to, as in the case of RAID3,

There is no need for Instead of having to involve the whole group in every small I/O operation as in RAID3, only two hard disks in the group (one data disk and one checksum disk) can be involved, which improves the I/O speed for small amounts of data.

RAID4 can also be used as a cross access system for randomly dispersed small amounts of data. Disadvantage: For randomly dispersed small data I/O, the fixed checksum disk becomes an I/O bottleneck, for example: transaction processing. For example, if you do two very small write operations, one on stripe1 of drive2 and one on stripe2 of drive3, they both have to write to the checksum disk, so there is contention for the checksum disk.

RAID5: RAID 5 - Striping with floating parity drive (most commonly used)

is a type of rotating parity array with independent access, which differs from RAID3 and RAID4 in that it doesn't have fixed parity disks, but instead evenly distributes parity information across the array's disks according to certain rules

. The parity information is distributed evenly across the hard disks that belong to the array, so that on each hard disk, there is both data and parity information. This change solves the problem of contention for parity disks

and allows multiple concurrent write operations within the same group. Therefore, RAID5 is suitable for large data volume operations as well as a variety of transaction processing, and it is a fast, large

capacity and fault-tolerance distribution of disk arrays. When there are N array disks, the user space is N-1 disk capacity. In RAID3 and RAID5, after a hard disk fails,

the RAID group changes from ONLINE to DEGRADED mode, but I/O reading and writing are not affected until the failed disk is recovered. However, if a second disk fails in the DEGRADED state, the entire

RAID group data will be lost.