| Much has been written about solid state disks | | | | coated disks, known as platters, that are |
| (SSDs) becoming the next big thing1 in the IT | | | | used to store data. This rotating motion of |
| industry(1). But as to whether or not we have | | | | the mechanical arms results in much wear and |
| enough knowledge of how it will revolutionize | | | | tear after long periods of use. The |
| the industry is a different question. How | | | | operational lifespan of a computer HDD is |
| much do we really know about SSDs? If we are | | | | over three years.(4) |
| to ask people on the streets, it wouldn't | | | | |
| come as a surprise that they dont know much | | | | |
| of what an SSD is. Even if they do know, most | | | | |
| probably it would be limited to a USB pen | | | | A Flash-based SSD is different. Although the |
| drive, a CompactFlash or a Secure Digital | | | | most common Flash chips have around 300,000 |
| card, which are more on the consumer side of | | | | write cycles, the best Flash chips are rated |
| the storage industry. | | | | at 1,000,000 write cycles per block. On top |
| | | | of that, Flash SSD manufacturers employ |
| | | | different ways to increase the longevity of |
| | | | the drives. In some cases, they use a |
| Technically speaking, they are not wrong. | | | | "balancing" algorithm to monitor the number |
| Most web definitions describe an SSD as a | | | | of times each disk block has been written, |
| high-performance plug-and-play storage device | | | | which greatly extends the operational |
| that contains no moving parts. Therefore, | | | | lifespan of the drive. Furthermore, these |
| given that most of the aforementioned mobile | | | | manufacturers also designed special |
| disk storage devices contain no movable | | | | "wear-leveling" algorithms where once a |
| parts, they can certainly be categorized as | | | | certain percentage threshold for a given |
| SSDs. | | | | block is reached, the SSD will swap the data |
| | | | in that block with the data in another block |
| | | | that has exhibited a "read-only-like" |
| | | | characteristic in the background. This |
| But then again, there's more to SSDs than | | | | reduces performance lag and avoids further |
| being a non-volatile device. The purpose of | | | | wearing off of the blocks and thrashing of |
| this article is to give readers a clearer | | | | the disk. Even with usage patterns of writing |
| picture of what an SSD is, its usage as well | | | | reading gigabytes per day, a Flash-based SSD |
| as its difference when pitted against the | | | | should last several years, depending on its |
| predominant data storage device at present - | | | | capacity. Add to that the inclusion of a DRAM |
| the hard disk drive (HDD). More than its | | | | cache in the disk architecture that further |
| non-volatility, this article will reveal how | | | | enhances its operational capabilities as well |
| much potential SSDs have in optimizing the | | | | as lifespan. |
| performance of the computing system. | | | | |
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| | | | Speeding Up |
| SSD Defined | | | | |
| | | | |
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| | | | With the very fast paced lifestyle these |
| Here are several ways the SSD is defined: | | | | days, most businesses are time-bound and |
| | | | cannot afford a slowing down in their |
| | | | transactions. This makes speed of HDDs a |
| | | | crucial point in technological purchases. The |
| "A solid state disk (SSD) is electrically, | | | | typical access time for a Flash based SSD is |
| mechanically and software compatible with a | | | | about 35 - 100 s, whereas that of a rotating |
| conventional (magnetic) hard disk or | | | | disk is around 5,000 - 10,000 s. That makes a |
| winchester. The difference is that the | | | | Flash-based SSD approximately 100 times |
| storage medium is not magnetic (like a hard | | | | faster than a rotating disk. |
| disk) or optical (like a CD) but solid state | | | | |
| semiconductor such as battery backed RAM, | | | | |
| EPROM or other electrically erasable RAM-like | | | | |
| chip. This provides faster access time than a | | | | This however raises another point - what's |
| disk, because the data can be randomly | | | | the benefit of a high-speed SSD when the |
| accessed and does not rely on a read/write | | | | entire system cannot support it? The |
| interface head synchronising with a rotating | | | | evolution of CPUs in terms of performance has |
| disk. The SSD also provides greater physical | | | | far surpassed the development of the data |
| resilience to physical vibration, shock and | | | | storage system. The HDD is actually limiting |
| extreme temperature fluctuations. The only | | | | the potential of a computer system when they |
| downside is a higher cost per megabyte of | | | | are not able to keep up with the performance |
| storage."(2) | | | | of the other components, particularly the |
| | | | CPU. If an HDD is replaced by a high-speed |
| | | | SSD, the performance would significantly |
| | | | improve. The resulting system would be a |
| "Abbreviated SSD, a solid state disk is a | | | | high-powered set-up that can go beyond the |
| high-performance plug-and-play storage device | | | | demands of high-speed business or military |
| that contains no moving parts. SSD components | | | | environments. |
| include either DRAM or flash memory boards, a | | | | |
| memory bus board, a CPU, and a battery card. | | | | |
| Because they contain their own CPUs to manage | | | | |
| data storage, they are a lot faster (18MBps | | | | Size Matters |
| for SCSI-II and 44 MBps for UltraWide SCSI | | | | |
| interfaces) than conventional rotating hard | | | | |
| disks ; therefore, they produce highest | | | | |
| possible I/O rates. SSDs are most effective | | | | To be a true plug-in replacement for HDDs, |
| for server applications and server systems, | | | | Flash-based SSDs are manufactured in standard |
| where I/O response time is crucial. Data | | | | 2.5" and 3.5" form factors. 2.5" SSDs are |
| stored on SSDs should include anything that | | | | normally used in laptops or notebooks while |
| creates bottlenecks, such as databases, swap | | | | the 3.5" form factors are used in desktops, |
| files, library and index files, and | | | | or in JBOD or other SAN/NAS/DAS |
| authorization and login information."(3) | | | | configurations. They can often be used to |
| | | | replace traditional disks in storage arrays |
| | | | or in a server's internal disk bays. |
| | | | Flash-based SSDs certainly fit the storage |
| For the rest of the article, we will compare | | | | needs of most embedded systems that require |
| the HDDs and Flash-based SSDs. The latter are | | | | much smaller form factors. |
| the most popular type of SSDs employed by the | | | | |
| military, aerospace, industrial and embedded | | | | |
| systems industries. | | | | |
| | | | Reliability |
| | | | |
| | | | |
| Mortality Rate | | | | |
| | | | In terms of reliability, conventional HDDs |
| | | | pale when compared to SSDs. The absence of |
| | | | mechanical arms and spinning platters is the |
| Hard disk failure is a common occurrence in | | | | reason behind its reliability. In demanding |
| this age of desktops and notebooks. A lot of | | | | environments, SSDs provide the type of |
| horror stories have been told, passed around | | | | ruggedness required for mobile applications. |
| and even published about how valuable data | | | | Unlike the HDD, SSD's can withstand extreme |
| was lost and the agony of trying to retrieve | | | | shock and vibration with data integrity and |
| or at least save a portion of the crashed | | | | without any danger of data loss. This feature |
| hard drive. It is during this time that | | | | is very important in industrial applications |
| people wonder, why do hard disks fail? | | | | where exposure to highly combustible |
| | | | materials and electromagnetic radiation are |
| | | | typical. Their ability to deliver unnerving |
| | | | performance in extreme conditions also makes |
| The reason is simple - wear and tear. Just | | | | SSD play a vital role in military operations, |
| like any good old machine with mechanical | | | | be it in defense, aerospace or aviation |
| components, HDDs tend to deteriorate over | | | | applications. |
| time. HDDs consist of rotating, magnetically | | | | |