What is SSD and its advantages and disadvantages?

What is SSD?

A Solid State Disk (Solid State Disk or Solid State Drive), also known as an electronic hard Disk or Solid State electronic Disk, is a hard Disk consisting of a control unit and a Solid State storage unit (DRAM or FLASH chip. The interface specifications, functions, and usage of SSD are the same as those of common hard disks, and the product shape and size are also the same as those of common hard disks. As solid state disks do not have the rotating media of common hard disks, they provide excellent shock resistance. The operating temperature range of the chip is very wide (-40 ~ 85 degrees Celsius ). It is widely used in military, vehicle, industrial control, video monitoring, network monitoring, network terminals, power supplies, medical, aviation, navigation equipment, and other fields. However, due to the high cost, it has not been popularized in the DIY market.

SSD category

SSD storage media are divided into two types: FLASH Memory (FLASH chip) and DRAM. Solid State Disks Based on FLASH memory (IDE Flash DISK and Serial ata flash Disk): FLASH chips are used as storage media, which is what we call SSD. Its appearance can be made into a variety of styles, such as laptop hard disks, micro-hard disks, memory cards, and USB flash drives. The biggest advantage of SSD is that it can be moved and data protection is not controlled by the power supply. It can be used in various environments, but its service life is not high. It is suitable for individual users. In SSD Based on flash memory, there are two types of storage units: SLC (Single Layer Cell Single Layer unit) and MLC (Multi-Level Cell Multi Layer unit ). The disadvantage of SLC is high cost, small capacity, and fast speed. MLC features high capacity and low cost, but slow speed. Each unit of MLC is 2bit, which is twice as much as that of SLC. However, because each MLC storage unit stores a large amount of data and the structure is relatively complex, the probability of errors increases and errors must be corrected, this action causes its performance to lag far behind the simple structured SLC flash memory. In addition, the advantage of SLC flash memory is that the number of rewrites reaches 100000 times, which is 10 times higher than that of MLC flash memory. In addition, in order to ensure the life of MLC, the control chip verifies and the smart wear Balancing Technology algorithm, so that the number of writes to each storage unit can be evenly shared to reach a fault interval of 1 million hours (MTBF ).

Internal Structure

DRAM-based solid state disks: DRAM is used as the storage medium, and the current application scope is narrow. It imitates the design of traditional hard disks and can be set and managed by File System Tools of most operating systems. It also provides industry-standard PCI and FC interfaces for connecting hosts or servers. The application methods can be divided into two types: SSD hard disk and SSD hard disk array. It is a high-performance memory with a long service life. What is lacking in the US is the need for independent power supplies to protect data security.

Advantages of SSD

SSD has the following advantages compared with general hard drive:

1. Fast start, no motor accelerated rotation process.

2. Fast random reading without a head, with minimal read latency. According to relevant tests: it takes only 18 seconds for a laptop with a solid state drive to start from the boot to the desktop on two computers with the same configuration, the laptop carrying a traditional hard drive took 31 seconds in total, nearly half of the gap between the two.

3. relatively fixed read time. Since the addressing time is irrelevant to the data storage location, disk fragments do not affect the read time.

4. DRAM-based SSD writes extremely fast.

5. No noise. Because there are no mechanical motors and fans, the noise value is 0 decibels at work. Some high-end or large-capacity products are equipped with fans, which still produce noise.

6. Low-capacity flash-based solid state disks consume less energy and less heat while high-end or large-capacity products consume more energy.

7. There are no mechanical moving components in the system, and no mechanical faults or collisions, impacts or vibrations will occur. In this way, normal use is not affected even when high-speed movement or even with flip skew, and the possibility of data loss can be minimized in the case of accidental drops of a laptop or collisions with hard objects.

8. Wider operating temperature range. A typical hard drive can only work between 5 and 55 degrees Celsius. Most SSDS can be in-10 ~ Working at 70 degrees Celsius, some industrial solid state disks are available at-40 ~ 85 degrees Celsius, or even a larger temperature range.

9. Low-capacity SSDs are smaller and lighter than hard drives of the same capacity. However, this advantage gradually decreases as the capacity increases. Up to 256 GB, solid state disks are still lighter than common hard disks of the same capacity.

Disadvantages of SSD

Compared with traditional hard drives, SSD has the following Disadvantages:

1. High costs. The price per unit of capacity is 5 ~ of the traditional hard disk ~ 10 times (based on flash), or even 200 ~ 300 times (based on DRAM ).

2. Low capacity. At present, the maximum capacity of Solid State disks is much lower than that of traditional hard disks. SSD capacity continues to grow rapidly. It is said that IBM has tested a 4 tb ssd.

3. Solid State disks are more vulnerable to adverse effects caused by some external factors, unlike traditional hard drives that are shielded in the faradha cage. Such as power failure (especially for DRAM-based solid state disks), magnetic field interference, and static electricity.

4. Limited write life (based on flash ). Generally, the flash memory write life is 10 thousand to 0.1 million times, and the specially crafted memory can reach 1 million to 5 million times. However, some parts of the file system (such as the File Allocation Table) during the lifetime of the entire computer) the number of writes will still exceed this limit. The dedicated File System or firmware can share the write location, so that the overall life of the SSD is more than 20 years.

5. SSD Based on flash memory is much slower to write than traditional hard disks, and is more susceptible to the impact of writing fragments.

6. It is difficult to recover the damaged data. In traditional disk or tape storage mode, if the hardware is damaged, some data may be saved through the current data recovery technology. However, if the solid state disk is damaged, it is almost impossible to use the current data recovery technology to retrieve data from the expired (especially DRAM-based), broken or broken chip.

7. According to the actual test, the laptop using SSD is idle or low-load, and the battery range is shorter than 2.5 inch of the traditional hard drive using rpm.

8. DRAM-based solid state disks consume more energy than traditional hard disks at any time, especially when power is off, otherwise data is lost.

9. According to the user's report, the low-cost mlc solid state disks run slowly in Windows operating systems than traditional hard disks. This is because the file system mechanism of the Windows operating system is not suitable for solid state disks. This problem does not occur in Linux.

Comparison between traditional hard drive and solid state drive

1. shockproof and anti-dropping: currently, traditional hard disks are disk-type, and data is stored in the disk sector. Solid State disks are made from flash memory particles (storage media such as memory, MP3, and USB flash drives). Therefore, solid state disks do not contain any mechanical components, in this way, normal use is not affected even when high-speed movement or even with flip skew, and the possibility of data loss can be minimized in the case of collision and shock. Compared with traditional hard drives, hard drives have absolute advantages.

2. Data Storage speed: from the evaluation data of the PConline evaluation room, the performance of SSD is more than doubled than that of traditional hard disks.

3. Power Consumption: SSD power consumption is superior to that of traditional hard disks.

4. Weight: SSD is lighter in terms of weight. It is 20-30 grams lighter than conventional 1.8 inch hard disks.

5. Noise: Since solid hardware is a non-mechanical component and flash memory chip, it has the characteristics of low calorific value and fast heat dissipation. Moreover, there is no mechanical engine and fan, and the working noise value is 0 decibels. Traditional hard disks are inferior.

6. Price: At present, the market price of 80 GB Intel SSD is about 4000 yuan. The price is enough to buy a few traditional hard disks with a capacity of 1 TB.

7. Capacity: The maximum capacity of SSD is only 256 GB, which is much different from that of traditional hard disks measured by TB.

8. Service Life: SLC has only 0.1 million read/write times, and the low-cost MLC has only 10 thousand read/write times. It has no advantage over traditional hard disks.