The difference between SSD and common hard disk

Source: Internet
Author: User

Solid-State hard disk storage medium is divided into two types, one is the use of flash memory (Flash chip) as a storage medium, the other is the use of DRAM as a storage medium.

  Solid-state hard disk based on flash memory

Flash-based solid-state drives (IDE flash disk, serial ATA flash disk): Flash chips are used as storage media, which is what we usually call SSDs. Its appearance can be made into a variety of shapes, such as: Notebook hard disk, micro-hard disk, memory card, USB flash drive and other styles. The biggest advantage of this SSD is that it can be moved, and the data protection is not controlled by power and can adapt to all kinds of environment, but the service life is not high, and it is suitable for individual users to use. In a solid-state hard disk based on flash memory, the storage unit is divided into two categories: SLC (single Layer cell) and MLC (multi-level cell multi-layer unit). SLC is characterized by high cost, small capacity, but speed, while MLC is characterized by low capacity, but slow speed. Each unit of the MLC is 2bit, a whole lot more than SLC. However, due to the large number of data stored in each MLC storage unit, the structure is relatively complex, the probability of error will increase, the error correction must be made, this action causes its performance significantly behind the structure of simple SLC flash. In addition, SLC flash memory has the advantage of 100,000 replication times, up to 10 times times higher than MLC flash memory. In addition, in order to ensure the life of MLC, the control chip is calibrated and the intelligent wear balance technology algorithm, so that each memory unit can be allocated to the average number of times, to achieve 1 million-hour failure interval (MTBF).

  Solid-state hard disk based on DRAM

DRAM based SSD: using DRAM as storage medium, the application scope is narrow. It follows the design of traditional hard disks, can be set up and managed by the file system tools of most operating systems, and provides industrial standard PCI and FC interfaces for connecting hosts or servers. The application method can be divided into SSD hard disk and SSD hard disk array two kinds. It is a high-performance memory, and the service life is very long, in the ointment is the need for independent power to protect data security.

  The advantages of solid-state drives:

1, start fast, no motor acceleration rotation process;

2, without head, Fast random reading, reading delay is very small;

3, relatively fixed reading speed, because the addressing time and data storage location independent, so disk fragmentation does not affect the read time;

4, write fast (based on DRAM), hard disk I/O operation performance is good, can significantly improve the need for frequent read-write system performance;

5, no noise;

6, the low capacity of the solid-state drive based on flash memory in the working state of energy consumption and heat is small, but high-end or large-capacity products higher energy consumption;

7, the possibility of mechanical error is very low, not afraid of collision, shock and vibration;

8, the working temperature range is big;

9, small size.

  The disadvantages of solid-state hard drives compared to traditional hard drives:

1, the cost is high, the maximum capacity is low;

2, because unlike the traditional hard drive as tired in the Faraday cage, solid-state drives are more likely to receive some of the adverse effects of external factors. such as power loss (especially based on DRAM solid-state hard disk), magnetic interference, electrostatic and so on.

3, Write Life is limited (based on Flash). General Flash write life of 10,000 to 100,000 times, the special can be large 1 million to 5 million times, but the entire computer lifetime period of the file system some parts of the written times will still exceed this limit;

4, data corruption difficult to recover. Once damaged on the hardware, if the traditional disk or tape storage mode, through data recovery may also save a part of the data. But if it's a solid-state store, and a chip is damaged, it's almost impossible to get the data back in a chip that breaks into several lobes or is penetrated by the current.

5, high energy consumption, based on DRAM solid-state hard disk at any time than the traditional hard drive, especially when the shutdown still need power, otherwise data loss.

  Comparison of the advantages and disadvantages of SSD and traditional hard disk 

  Project Solid State Drive Traditional Hard Drive              

Small size

Price level

Random Access extremely fast general

Write Count Slc:10 million times unlimited

Mlc:1 million times

Disk array can be extremely difficult

No noise at work

Working temperature is very low and obvious

Shockproof is very good poor

Data recovery is difficult to

Weight and severity

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