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Solid State Drive Frequently Asked Questions (FAQs)
1. Are solid state drives becoming affordable for mainstream computing?
Today, the proven performance of MLC NAND-based SSDs is enabling more consumer-oriented prices. SSDs for notebook computers are most suitable for users who value increased reliability, ruggedness and performance.
Like many new technologies, SSDs for mainstream computing applications carry a price premium in comparison to the standard solution, in this case, hard disk drives.
However, as SSD prices continue to decline, this price premium will decrease, too. Use of Multi-level Cell NAND, which stores two or more bits per cell, advances in NAND process technology and the expected price curve for semiconductor memory products will continue to improve the value/performance of MLC SSDs. In 2009 and 2010, the notebook computing market is expected to show increased adoption of SSDs, growing to approximately 17% of the notebook market by 20131.
The important thing when choosing MLC vs. SLC SSD is to have the right technology for the right application. Based on our usage modeling, Toshiba finds that MLC-based SSDs are a good fit for most mobile computing applications, while SLC-based SSDs are usually better suited for high performance enterprise applications.
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2. What are the advantages of solid state drives?
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GRAPHICS: Benchmark PCmark05
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SSDs outperform HDDs in boot-up time, random read and write, and when opening and saving files.
Compared to hard disk drives, SSDs realize a number of advantages that address needs in the mobile computing market for performance, ruggedness, and lightweight, compact form factors. Boot time is typically about half that required for an HDD. The time to find a file on the drive is measured in millionths of a second for SSDs and in thousandths of a second for HDDs, so the difference adds up.
The benchmark scores (see link above) for Toshiba MLC NAND SSDs1 show the performance advantages of our 43nm SSDs compared to 5400 rpm and 7200rpm HDDs. These SSDs excel Windows® XP boot speed, application loading, general usage and virus scan.
Perhaps even more important to the mobile user are the advantages in terms of higher reliability and ruggedness. Because they have no moving parts, SSDs can withstand greater shock and vibration, and have the added benefit of quieter operation. According to Web-Feet Research2, 2.5-inch hard drives for computing applications can withstand 350Gs of operating shock and 900Gs of non-operating shock, while NAND-based SSDs can withstand >1500Gs for both operating and non-operating shock. For vibration resistance, 2.5-inch drives can withstand 0.7Gs vibration, while both MLC and SLC NAND-based SSDs can withstand 20Gs or more.
As an added benefit, SSDs can also be configured to smaller form factors and reduced weight compared to hard drives.
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3. How do SSDs vary in performance, and what features should I look for?
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GRAPHICS: MLC NAND Leadership
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Many benchmarks have shown that there can be a significant difference in performance from one SSD to another. Buyers should carefully consider the drive manufacturer's experience in NAND manufacturing and technology as well as the specific features and performance of the drives they consider.
Not all SSDs are created equal. Just taking a controller and NAND and putting it in a drive enclosure does not make a successful SSD. The early market indications that not all SSDs are meeting expectations can be attributed in part to this concern.
We believe that three factors are critical: the design of the controller, proven NAND flash technology and experience with the hard disk drive market. The architecture of the controller can have a significant impact on endurance, wear-leveling and performance, and SSD architectural features such as DRAM cache and parallel design are critical to better performance, but are not apparent to the end user. As an innovator of NAND flash since the 1980's, Toshiba has found that experience plays a significant role in maintaining quality and yield with each process migration as well as in moving to multi-level cell technologies to store more than one bit per cell. Toshiba's SSD products are unique in the industry as they are a collaborative effort developed with expertise from both storage and semiconductor businesses, designed to meet the requirements of the mobile PC OEM and the ultimate end user and deliver Toshiba SOLID performance. |
4. What is the endurance limit of a solid state drive? Do MLC NAND-based SSDs "wear out" if you write a lot of data? How do I determine the endurance requirements for my application?
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GRAPHICS: Daily Average Write Limit by Capacity | Toshiba Usage Model Study
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The five-year estimated write capacity of a 128GB1 Toshiba MLC SSD is 80 Terabytes2, well beyond the typical usage of a mobile computer user. Users with unusually large write requirements can increase write capacity by choosing a larger capacity SSD.
It's true that MLC NAND drives are rated for a smaller number of write cycles than SLC NAND-based drives, but the important thing when choosing MLC vs. SLC is to have the right technology for the right application. Based on our usage modeling, Toshiba believes that MLC-based SSDs are a good fit for most mobile computing applications, while SLC-based SSDs may be better suited for high-performance enterprise applications.
Absent any industry standard usage model, Toshiba developed an internal model and studied usage patterns for normal and heavy, or write-intensive, users. To even begin to reach a conservative endurance limit of a 64GB MLC NAND-based SSD with wear-leveling technology, a mobile user would have to write approximately 40 Terabytes (forty trillion bytes) of data over the expected five-year life of the drive. That's equal to approximately 22GB of new data per day, every day – or enough to fill 4.6 DVDs, or 32 CDs daily. With a 128GB drive, for example, the wear would be spread over a larger storage area, effectively doubling the average daily write limit to 44GB, or more than 9 DVDs. In the Toshiba usage modeling study*, typical users wrote approximately 1.4GB/day, and heavy users wrote about 5.2GB/day. Further analysis showed that auto-save and hibernate features could increase total data written per day to 2.4GB for the typical user and 9.2GB for heavy users. Although the specifications of Toshiba 64GB MLC SSDs exceed the 40 Terabyte example provided, it may help demonstrate that the endurance limit is so far beyond the likely usage of a typical mobile computer user that it isn't a realistic cause for concern.
Toshiba also compared the daily write volume for PC-class SSDs using MLC and SLC technology. For a 128GB SLC NAND drive, the daily write volume increases to approximately 500GB per day over a 5-year life, while the 256GB and 512GB drives could support write volumes of 1 and 2 Terabytes per day, respectively.
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5. Are SSDs more reliable or rugged than hard disk drives? How does an SSD handle error correction compared to a hard disk drive?
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GRAPHICS: Error Correction
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With no mechanical parts, SSDs are less likely to suffer unexpected drive failure than HDDs. Both SSDs and HDDs use error correction to provide virtually error free storage. The defacto industry standard for SSDs is to correct bit errors to a level comparable to that of HDDs.
Overall, both MLC and SLC types of SSD have no mechanical parts so they are not prone to mechanical failure, and typically have a higher rated MTTF than HDDs1. This additional ruggedness and reliability is the reason flash-based SSDs have been used since the mid-1990's in military and mission-critical applications and are now gaining in popularity for mobile computer users.
Both HDD and MLC NAND SSD drives utilize error correction algorithms to ensure that data is stored safely. Just as a hard disk drive is widely accepted with little concern about bad sectors, the NAND flash memory in a SSD works in a similar way in that the controller maps around bad memory areas and error correction code (ECC) is used to correct bit errors. Controllers for NAND flash have built-in ECC to automatically correct bit errors. The defacto industry standard is to correct any bit error to a level comparable to that of hard disk drives. System designers have long been aware of using ECC to detect and correct errors. Historically, memory subsystems have used Hamming code, while Reed Solomon ECC is common in hard drives and CD-ROMs.
MLC NAND-based SSDs do require more complex error correction than those using SLC NAND, but this function is taken care of by the integrated controller, and is transparent to the user.
Industry observers have noted that Total Cost of Ownership may be reduced with SSDs, with savings coming from lower support and replacement costs, as well as reduced costs for recovering data from a failed hard drive, and reduced productivity losses due to time without a PC.
For more information on drive endurance, or estimated write capacity, please see Myth 4.
HDDs are generally expected to last three to five years, and Toshiba SSDs are designed to match this level of performance, both in endurance and data retention. For all storage solutions, best practices for data management recommend backing up your data.
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6. What are the differences between Toshiba's families of SSDs, and what capacities are offered?
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GRAPHICS: 512GB Solid State Drive
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SSDs are now available in many capacities, including high-capacity Toshiba drives of 256GB and 512GB for mobile computer users, as well as the highest capacity, 128GB mSATA and Half-Slim modules for mini-mobile and netbook PCs.
Toshiba offers one of the only 512GB SSDs currently shipping, and was one of the first companies as one of the first companies to market with a family of products based on MLC NAND technology. Toshiba offers its high performance HG Series SSDs for high-end notebooks in 128GB, 256GB and 512GB capacities, in 1.8-inch and 2.5-inch form factors, including a slim 7mm thin version of the 2.5-inch drive. Capacities for SSDs are not expected to be a limiting factor as value/performance improves with advances in NAND technology combined with the historical price decline in semiconductor storage. The HG3 Series enable improved system responsiveness with a maximum sequential read speed of 240 to 250MB per second (MBps) and maximum sequential write speed of 180MBps.
Our SG series mSATA and Half-Slim SSD modules using 32m MLC NAND Flash are available in 30, 62 and 128GB capacities. These two module form factors, each smaller than a business card, enable mobile computing devices. The SG Series features a maximum sequential read speed of 180MBps and a maximum sequential write speed of 70MBps. The 128GB modules are only one seventh the volume and one eighth the weight of a 2.5-inch standard form factor SSD, and consume a fraction of the power. |
7. What is TRIM Support, and do Toshiba SSDs support it?
The TRIM Command allows an operating system (OS) that supports it, such as Windows 7, to send information to a solid state drive controller to tell it which data blocks are no longer in use and can be deleted. An OS operation such as delete in the past or with operating systems that don't support the TRIM command means the data blocks involved are flagged as not in use but not actually deleted. TRIM allows the OS to pass this information on down to the SSD controller, so the data is removed before the next time the drive may need to write to those blocks.
The purpose of the instruction is to maintain the speed of the SSD throughout its lifespan, avoiding the slowdown that early models encountered once all of the cells had been written to once.
Toshiba's new 32nm HG3 and SG2 Series support the TRIM Command implemented in Windows 7.
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8. Do solid state drives require less power? Will this extend battery life?
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GRAPHICS: WW Energy Savings Using SSDs | SSD vs. HDD Power Consumption
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Because solid state drives do not require a motor, they consume less power than hard disk drives, which helps extend system battery life. In a Toshiba study, comparing a Toshiba solid state drive and a typical 2.5-inch hard disk drive, the SSD consumed at least 20% less power1. SSDs provide a noticeable reduction in power consumption, but because the system processor and display use much more power, the difference may not extend the battery life of a mobile computer in all cases.
According to a study by market analyst firm Web-Feet Research2, SSD drives with SATA interfaces for PC applications typically consume 0.5W during read and 1.0W during write operations compared to 2.0W read/1.8W write for 5400 rpm 2.5-inch HDDs, and 2.3W read/2.1W write for 7200 rpm 2.5-inch SSDs. This means that for read operations, SSDs consume about 75% less power than HDDs, and for write operations, about 50% less. However, there are very low power 1.8-inch hard drives on the market that reduce these differences.
For enterprise applications, solid state drives offer the potential to reduce power consumption significantly compared to HDDs. In some cases, where short stroke HDDs are used for very fast read and write applications, SSDs that use approximately 7W of power can replace one or more HDDs that use approximately 14W3. iSuppli forecast that the worldwide power savings from replacement of short-stroke HDDs by SSDs could increase from 6,986-megawatt hours in 2008 to 57,564 in 2013, a total savings of 166,643-megawatt hours over the six-year period, or enough to power a small country3. In addition, IDC analyzed the power consumption in data centers, and determined that for every watt used to power the actual drive, one additional watt is typically needed to cool the data center and another watt is required to power related electronic equipment (e.g. controllers, fans, host bus adapters and power supplies)4. With no moving parts, SSDs require less power and generate less heat, as shown in the SSD vs. HDD Power Consumption chart above. SSDs are attractive for enterprise applications because of faster random read and random write performance, and the ability to reduce related energy costs in the data center.
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9. Are SSDs replacing hard drives in mobile computers, or is there a trend to use the two types of drive together?
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GRAPHICS: 5 Fold Growth in 4 Years | Information vs. Available Storage
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SSDs and HDDs will continue to coexist in the market and in some cases may be used together.
There is a definite market opportunity for the performance and reliability advantages of SSDs. However, we expect SSDs to coexist with HDDs for the foreseeable future because there is a role for both storage technologies. Toshiba and market analysts expect SSDs to begin to gain significant traction in the market in 2009, growing to approximately 17% of the notebook market by 20131. Toshiba expects the value/performance of its MLC NAND-based SSD line-up to help speed the acceptance of solid state storage among early adopters of notebooks and ultra-mobile PCs (UMPCs).
According to IDC, digital storage is growing at a phenomenal pace. In 2008, 486 exabytes (that's 486 billion gigabytes) of digital data was created, captured and replicated, generated by over one billion devices including digital cameras, camera phones, medical scanners and surveillance cameras, as well as computers. By 2012, digital data is expected to grow five-fold to approximately 2,502 exabytes2. Major contributors to this growth include film to digital image capture, analog to digital voice, analog to digital TV, Internet, email and IM. In this vast storage market, there's plenty of room for both hard disk drives and SSDs, to provide choices for optimal retrieval of stored data.
Toshiba is an industry leader in both small form factor HDDs and in NAND flash-based SSD technology, and offers a broad selection of digital media products based on different storage technologies. The breadth of products and markets in which these solutions play shows Toshiba's insight into the requirements, possibilities and future directions of the quickly changing landscape for storage technologies. In the end, we see HDD and SSDs as critical storage solutions with long term viability and attributes specific to different applications.
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