RAID introduction, RAID 5

RAID introduction, RAID 5

　　

I. Introduction to RAID

Disadvantages of traditional disks: Poor IO performance and poor stability.

Components that affect computer performance generally include: CPU, motherboard bus IO, memory IO, hard disk IO, and nic IO. Modern computer bus and memory speed can reach 5 Gbps or even higher, but hard disk IO is often low, hard disk is the performance bottleneck of most computers.

RAID (Redundant Array of Independent Disks) Independent Redundant disk Array technology improves the storage I/O performance of computers by running multiple Disks in parallel. Prevents physical damage to hard disks and increases the throughput of storage devices.

Ii. RAID Classification

There are three types of Disk Arrays: External disk array cabinets, internal disk array cards, and simulation using software.

Iii. RAID principles

The disk array acts as an independent system and is directly connected to the Host outside the host or through the network. The disk array has multiple ports that can be connected by different hosts or ports. A host can be connected to an array of ports to increase transmission speed.

Like the integrated cache in a single disk in a PC at that time, a certain amount of buffer memory is provided in the disk array to speed up interaction with the host. The cache interaction between the host and the disk array, and the interaction data between the cache and the specific disk.

In applications, some common data needs to be read frequently. The disk array searches for frequently read data based on internal algorithms and stores the data in the cache, the speed for the host to read the data is accelerated. If the host does not read data from other caches, the array will directly read the data from the disk and transmit it to the host. For data written by the host, it is only written in the cache, and the host can immediately complete the write operation. Then, the cache writes data to the disk.

Iv. RAID level

RAID0: a minimum of two hard disks are used. During reading and writing, data is read and written separately to multiple hard disks to improve Read and Write Performance. It effectively improves the performance and throughput of the hard disk, but does not have data redundancy and error repair capabilities.

 

 

 

 

 

 

 

 

 

 

Space Utilization: sum of all hard disk space

Performance: Sum of the speed of all hard disks

Redundancy: None

RAID1: use at least two hard disks. When writing data, copy the data to multiple hard disks. To provide redundancy when reading data. Read data from multiple hard disks at the same time to improve read performance. This effectively improves the security and maintainability of data.

As shown in, the "parity" Block stores the parity information of other hard disk data (not the data of other hard disks), and uses the parity information to ensure data security, RAID5 does not store the data parity information on a separate hard disk, but is stored on each disk. In this way, when a hard disk is damaged, the damaged data can be re-built based on the parity information of other hard disks. The performance is also high, taking into account the storage performance, data security and storage costs, it can be seen as a compromise between RAID0 and RAID1.

Space Utilization: 1-1/n

Performance: The read performance is close to RAID0, And the write performance is weaker than RAID0.

Redundancy: one hard disk can be damaged.

RAID10: requires at least four hard disks, both read and write performance and security. It inherits the read/write performance of RAID0 and the security of raid1. RAID1 provides redundant backup, while RAID0 provides read/write performance.

 

Space Utilization: 1/2

Performance: Sum of the speed of all hard disks

Redundancy: each group of RAID 1 is allowed to damage one hard disk.

5. RAID implementation

Software RAID

RAID is implemented through system functions or RAID software without independent hardware and interfaces, which requires a certain amount of system resources (CPU and hard disk interface speed) and is affected by the operating system stability.

Hardware RAID

Using an independent RAID hardware card, some boards integrate RAID hardware, and some need to purchase an independent RAID hardware card. Hardware RAID does not need to occupy other hardware resources. The stability and speed are better than software RAID.