Because SSD technology is different from traditional hard disk technology, it has generated a number of emerging memory manufacturers. Manufacturers simply buy NAND memory and match it with the appropriate control chip to make SSDs. The new generation of SSDs commonly use the SATA-2 interface.
[edit][1][2]Classification
There are two types of storage media for SSDs, one using flash memory (FLASH chips) as the storage media, and the other using DRAM as the storage media.
Flash-based SSDs (IDE FLASH DISK, Serial ATA Flash Disk): Using FLASH chips as the storage medium, this is what we usually call an SSD, which can be made to look like a variety of models, such as laptop hard drives, microdisks, memory cards, flash drives, and other styles. The biggest advantage of this kind of SSD solid state drive is that it can be moved and the data protection is not controlled by the power supply, it can be adapted to a variety of environments, but the service life is not high, which is suitable for individual users. In flash-based SSDs, the storage cells are divided into two categories: SLC (Single Layer Cell) and MLC (Multi-Level Cell).SLC is characterized by high cost, small capacity, but fast speed, while MLC is characterized by high capacity and low cost, but slow.MLC is 2bit per cell, which is a whole lot more than SLC. MLC is 2 bits per cell, which is exactly twice as much as SLC. However, due to the large amount of data stored in each MLC memory cell, the structure is relatively complex, the chance of error increases, and error correction must be performed, which causes its performance to lag behind that of the simple SLC flash memory. In addition, the advantage of SLC flash memory is that the number of rewrites is up to 100,000 times, which is 10 times higher than MLC flash memory. In addition, in order to ensure the longevity of MLC, the control chip are checksum and intelligent wear leveling technology algorithms, so that the number of writes to each memory cell can be evenly spread to reach 1 million hours between failures (MTBF).
DRAM-based SSD: DRAM is used as the storage medium and is currently used in a narrower range of applications. It emulates the design of a traditional hard drive, can be configured and managed by the file system utility of most operating systems, and provides industry-standard PCI and FC interfaces for connecting to host computers or servers. Applications can be categorized into SSD drives and SSD drive arrays. It is a high-performance memory and has a long service life, the beauty of which is that it requires a separate power supply to protect data security.
[edit]Advantages of SSD
SSDs have the following advantages over regular hard disks:
1. Fast startup, no motor to accelerate the spinning process.
2. No magnetic heads, fast random reads with minimal read latency. According to the relevant tests: two computers in the same configuration of the computer, equipped with a solid state hard disk laptop from boot to appear desktop a *** only 18 seconds, while equipped with a traditional hard disk laptop with a total of *** with 31 seconds, the two almost have almost half of the gap.
3. Relatively constant read times. Since addressing time is independent of where the data is stored, disk fragmentation does not affect read times.
4. DRAM-based SSDs are extremely fast to write to.
5. No noise. Because there is no mechanical motor or fan, the noise level is 0 dB during operation. Some high-end or high-capacity products are equipped with a fan, so noise is still generated.
6. Low-capacity flash-based SSDs consume less energy and generate less heat during operation, but high-end or high-capacity products consume more energy.
7. There are no mechanical moving parts inside, so there is no mechanical failure and no fear of collision, shock, or vibration. This will not affect the normal use of the laptop even if it is moved at high speed or even tilted with a flip, and will minimize the possibility of data loss when the laptop accidentally falls or collides with hard objects.
8. Higher operating temperature range. Typical hard drives only operate in the 5 to 55 degree Celsius range. Most SSDs can operate at -10 to 70 degrees Celsius, and some industrial-grade SSDs can operate at -40 to 85 degrees Celsius and beyond.
9. Low-capacity SSDs are smaller and lighter than drives of the same capacity. However, this advantage diminishes as the capacity increases. Up to 256GB, SSDs are still lighter than regular hard drives of the same capacity.
[edit]Disadvantages of Solid State Drives
Solid State Drives have the following disadvantages compared to traditional hard drives:
1. High cost. The price per unit of capacity is 5 to 10 times (flash-based) or even 200 to 300 times (DRAM-based) that of a traditional hard disk.
2. Low capacity. The current maximum capacity of SSDs is much lower than that of traditional hard disks. The capacity of SSDs is still growing rapidly, and IBM has reportedly tested a 4TB SSD.
3. Because they are not shielded in a Faraday cage like traditional hard drives, SSDs are more susceptible to the adverse effects of certain external factors. For example, power outages (especially in DRAM-based SSDs), magnetic interference, static electricity, and so on.
4. Limited write life (flash-based). Typical flash memory has a write life of 10,000 to 100,000 cycles, and specialized ones can have a write life of 1,000,000 to 5,000,000 cycles, but some parts of the file system (such as the file allocation table) will still be written to more than that throughout the life of the computer. A purpose-built file system or firmware can share the write location, allowing the SSD to have an overall lifespan of 20+ years.
5. Flash-based SSDs are much slower to write and more susceptible to write fragmentation than traditional hard drives.
6. It is difficult to recover from data corruption. Traditional disk or tape storage, if the hardware is damaged, through the current data recovery technology may still be able to save part of the data. However, if a solid state drive is damaged, it is virtually impossible to recover data from a failed (especially DRAM-based), broken, or punctured chip with current data recovery techniques.
7. Based on real-world testing, laptops with SSDs have shorter battery life than 2.5-inch traditional hard drives with 5400RPM, when running at idle or low load.
8. DRAM-based SSDs consume more power than traditional hard drives at all times, especially when they are turned off and still require power or data loss.
9. According to users, SSDs using inexpensive MLCs run slower than traditional hard drives under Windows operating systems. This is due to the fact that the file system mechanism of Windows OS is not suitable for SSDs. This is not a problem with Linux.
[edit]SSD products
Existing SSD products are 3.5-inch, 2.5-inch, 1.8-inch and other types, with a capacity of 16~256GB, which is larger than a general flash drive (USB flash drive). The interface specifications are the same as the traditional hard disk, with UATA, SATA, SCSI and so on.
At CES 2008, professional SSD maker BitMicro Networks showed the internals of a professional-grade SSD product with a SCSI interface (see right). The product has 32 TSOP-packaged NAND flash memory chips soldered to a single PCB. BitMicro revealed that the average price per GB of the product is about $10, about five times that of a mainstream mechanical hard disk.
Lanxite also launched what it called the "first domestic" SSD in 2008. The company's first solid-state drive was launched in 2007, and the company claims to have launched the first solid-state drive in China. The next step is to launch the "world's fastest" SSD products, and Magnesium can be said to have launched a speed of 1GB / S SSD (with SSDs as an array).
Limitations of SSD solid state storage
While S S D seems to be vastly superior to disk technology, there are some drawbacks. First it is expensive, as memory costs almost 1 0 0 times as much as disk storage. Secondly, they usually consist of volatile D R A M , and in the event of a power failure, the data is permanently lost. To avoid data loss, S S Ds should be protected by a battery backup. Finally, because the S S D is not a cache, instead of flushing a small number of data blocks to nonvolatile storage, it copies the entire contents of the S S D . While the capacity and the transfer rate for sustained writes varies for the target disk drive or subsystem, a reasonable estimate for this operation is 1 G B / m i n.
One way to manage this is to use the disk drive to mirror the S S D. However, there is additional overhead to handle the I / O of the mirrored drive, which negatively affects the overall I / O transfer rate of the S S D . But in any case, at least the time it takes to complete a mirror write operation to a mirrored disk is minimal.
For some reason, including chip density, thermal performance, and so on, S S Ds will always have less capacity than disk drives. When the disk subsystem is considered, the capacity difference is even more dramatic. This means that applications using S S Ds are limited by the storage capacity of the S S Ds. However, it is worth pointing out that S S Ds can be used in disk subsystems to provide high performance storage.
To summarize, higher selling prices have hindered the popularity of SSDs, which are several or even tens of times more expensive than mechanical hard drives of the same capacity.
Currently, the capacity of SSDs is smaller, and the maximum capacity of SSDs is only 128GB, compared to the current 500GB or even TB hard drives. The lack of endpoint support is also another major problem for SSDs.
Although SSDs are still subject to cost and capacity constraints, with the popularity of the Vista operating system, SSD specifications are constantly being upgraded and the development speed will be further accelerated, so SSDs will still be available tomorrow.
Comparison of the advantages and disadvantages of traditional hard drives and solid state drives
1, shock resistance: the current traditional hard drive are disk-type, data storage in the disk sector. And solid state hard drive is the use of flash memory particles (i.e., the current memory, MP3, U disk and other storage media) made, so the SSD solid state hard drive does not have any mechanical parts inside, so that even in high-speed movement or even accompanied by flipping tilt will not affect the normal use of the situation, and in the event of collision and shock can minimize the possibility of data loss. Compared to traditional hard drives, solid hard drives have an absolute advantage.
2, data storage speed: From the PConline evaluation room review data, the solid state hard disk relative to the traditional hard disk performance increased by more than 2 times.
3, power consumption: The power consumption of solid state drives is also higher than that of traditional hard drives.
4. Weight: SSDs are lighter in weight, 20-30 grams lighter than conventional 1.8-inch hard drives.
5, noise: because the solid hard belongs to no mechanical parts and flash memory chips, so with a small amount of heat, heat dissipation, etc., and there is no mechanical motor and fan, the working noise value of 0 decibels. The traditional hard disk is much inferior.
6, price: the current market 80G Intel SSD, the price is about 4000 yuan. And this price is enough to buy a few traditional hard disk with a capacity of 1TB.
7, capacity: solid state drive maximum capacity of only 256G (IBM has begun testing capacity of 4TB high-speed solid state drive group), and the traditional hard disk maximum capacity measured by TB compared to a large gap.
8, life: SLC only 100,000 times read and write life, low-cost MLC, read and write life of only 10,000 times; compared to traditional hard disk has no advantage to speak of.
Solid-state drive security
Solid-state disk drives may offer better data security than traditional hard drives, but experts say they don't erase data completely and are less resilient to physical attacks from Light Sources high-output-type lamps like UV lasers. Despite their relatively high cost and better durability, solid-state disk drives are popular, especially in portable computers, because they feature low power consumption and fast data access. Experts say that securing data on solid state disk drives will become more of a concern as the technology becomes more widely used and penetrates other handheld devices such as smartphones.
Jim Handy, president of Objective Analysis, a semiconductor research and consulting firm, said that many solid-state disk drives use industry-standard NAND flash chips designed for camcorders and MP3 players, so they do not have physical security vulnerabilities that would prevent them from being transferred from the storage container (Enclosure). A hacker could easily detach the NAND chip from the solid-state disk drive and then use a flash chip program to read the data on it.
Once the data has been read, data recovery software can be used to reorganize the files, Handy said, "There's really nothing complicated about the process."
Bunnie, a hacker who specializes in attacking chips at the blog site bunnie studios, said another physical attack involves using an ultraviolet laser to remove the lockbit, or cryptolocker ---- which sits on the chip's fuse and is used to protect solid-state disk drives. After the lockbit is removed, arrays of data on the SSD can be read using standard methods.
Bunnie said, "Once the data is unlocked, it doesn't take any special equipment at all to be able to read that data array." For example, the data array can be read using a regular ROM reader, a device that usually means burning and verifying an insecure ROM device.
To reduce the likelihood of hackers stealing data, crypto locks can be integrated inside solid-state disk drive controller devices and used to address disk encryption from the hardware layer, said Craig Rawlings, director of marketing at Kilopass, which sells products that use super-permanent programmable memory (XPM) technology on system-on-chip devices to storage encryption locks on a system-on-chip device.
While encryption locks can be attacked, experts agree that encryption is a top priority for securing data on solid-state disk drives. Many companies, including Safend and Encryptx, have products in this area that encrypt data on storage devices such as SSDs.
Sean Barry, senior engineer of data recovery at Kroll Ontrack, said that encryption adds yet another line of defense, so hackers have to bypass the encryption layer and the controller, and then reorganize the original data so they can successfully steal it. This takes a certain amount of time, during which time the data is likely to be invalid or worthless.
Encryption also makes it easier to erase files on solid-state disk drives. iFixlt's CEO, Kyle Wiens, said that, like hard disk drives, while SSDs create multiple backups of files, encryption software can help you erase protected files.
Wiens said, "Every time you write data to an SSD, it's possible that it writes to another part of the drive and then modifies the directory table. In this way, it forgets the address where the data was previously stored." A user might delete a file, but a copy on another partition might still be safe and sound.
Wiens said that the wear-leveling feature of solid-state disk drives (based on a certain algorithm) evens out and writes data across all of the storage chip units, thus equalizing the aging rate across the storage chip units, making it harder for files to be completely erased.
Intel Fellow - Knut Grimsrud said that some encryption software monitors the wear-leveling process to track traces of files, which can then be removed using the Secure Erase command. Secure erase is a command for securely deleting files that requires support from encryption software.
Grimsrud said, "If all the software is writing data at the top level of Logical Block Addressing (LBA), I think it may not be very efficient on solid-state disk drives because it may have lost the previous efficiency gains from loss balancing or other similar features and the software doesn't know that. " Logical block addressing (LBA) specifies the address where data blocks are stored on a storage device.
In summary, it is easier to delete data on a solid-state disk drive than it is on a hard disk drive, which has its good and bad points, said KrollOntrack's Barry, adding that the data is stored on the tubes of the solid-state disk drive, and by eliminating the tubes, the data is flushed out. On hard disk drives, on the other hand, the data has to be overwritten or suffer physical damage in order to prevent it from being read.
Barry said that data flushing has its own advantages from a fast point of view, but from a bad point of view, data on solid-state disk drives tends to be more random and easily lost.