المعرفة

محرك أقراص الحالة الصلبة

"SSD" تحوّل إلى هنا. لمطالعة استخدامات أخرى، انظر SSD (توضيح).
"قرص إلكتروني" تحوّل إلى هنا. لمطالعة استخدامات أخرى، انظر قرص إلكتروني (توضيح).

محرك أقراص الحالة الصلبة أو القرص الإلكتروني solid-state drive (SSD)، هو جهاز تخزين الحالة الصلبة يستخدم تجميعات الدوائر المتكاملة كذاكرة لتخزين البيانات بشكل متزامن. كما يسمى أحياناً قرص الحالة الصلبة solid-state disk،[1] كلمة "قرص" غير مناسبة حيث أن محركات أقراص الحالة الصلبة ليست أقراص بالمعنى المادي. تستخدم محركات أقراص الحالة الصلبة واجهات محرك القرص الصلب، مثل ساتا وساس، التي تبسط بشكل كبير استخدام محركات أقراص الحالة الصلبة في الحاسوب.[2] في أعقاب القبول المبدئي باستخدام محركات أقراص الحالة الصلبة مع واجهات محركات القرص الصلب، تم تصميم الواجهات الجديدة مثل إم.2 ويو.2 لتلبية بعض المتطلبات لتكنولوجيا ذاكرة الفلاش المستخدمة في محركات الأقراص الصلبة.

محرك أقراص الحالة الصلبة
Super Talent 2.5in SATA SSD SAM64GM25S.jpg
محرك أقراص الحالة الصلبة من إنتاج سوپر تالنت تكنولوجي 2.5.
تاريخ الاختراع1978
المخترعشركة ستوردج تكنولوجي
A PCI-attached IO Accelerator SSD
An mSATA SSD with an external enclosure
Samsung SSD 960 PRO 512GB

لا تتضمن محركات الأقراص الصلبة مكونات ميكانيكية متحركة. يميزها هذا عن محركات الأقراص الكهروميكانيكية التقليدية مثل محركات الأقراص الصلبة أو الأقراص المرنة، والتي تحتوي على أقراص دورانية وread/write heads متحركة.[3] مقارنة بمحركات الأقراص الكهروميكانيكية، فمحركات أقراص الحالة الصلبة أكثر مقاومة للصدمات المادية، تعمل في صمت، تتمتع بزمن ولوج أسرع وكمون أقل.[4] ومع ذلك، فبينما يستمر سعر محركات أقراص الحالة الصلبة في الانخفاض بمرور الوقت، فلا يزال هناك محركات أقراص الحالة الصالبة الأغلى ثمناً لكل وحدة تخزين مقارنة بمحركات الأقراص الصلبة ومن المتوقع أن تستمر في الارتفاع في العقد القادم.

منذ 2017، معظم محركات الأقراص الصلبة تستخدم 3D TLC NAND-based flash memory، وهي أحد أنواع الذاكرات المستديمة التي تحتفظ بالبيانات عند انقطاع الطاقة. من أجل التطبيقات التي تتطلب سرعة ولوج لكنها لا تحتاج لتزامن البيانات بعد انقطاع الطاقة، يمكن إنشاء محركات أقراص الحالة الصلبة من ذاكرة الولوج العشوائي. قد تستخدم مثل هذه الأجهزة البطاريات كمصدر مدمج للطاقة من أجل الاحتفاظ بالبيانات لفترة زمنية معينة بعد إنقطاع الطاقة الخارجية.[2]

إلا أن جميع محركات أقراص الحالة الصلبة لا زالت تخزن البيانات في الشحنات الكهربائية، والتي تتسرب ببطئ مع الوقت إذا تركت بدون مصدر للطاقة. قد يتسبب هذا في تلف محركات الأقراص (التي تجاوزت تصنيف التحمل) لبدء فقدان البيانات والذي عادة ما يحدث بعد عام (إذا تم التخزين في درجة حرارة 30 °س) أو عامين (عند 25 °س)، وفي حالة محركات الأقراص الجديدة يتطلب وقتاً أطول.[5] وبالتالي فمحركات أقراص الحالة الصلبة غير ملائمة للأغراض الأرشيفية.

محركات الأقراص الهجينة أو محركات أقراص الحالة الصلبة الهجينة، مثل درايڤ فوجن من أپل، يجمع بين مميزات محركات أقراص الحالة الصلبة ومحركات الأقراص الصلبة في نفس الوحدة، والتي تحتوي على محرك أقراص صلبة ضخم ومحرك أقراص الحالة الصلبة من أجل تحسين أداء البيانات التي يتم الوصول إليها بشكل متكرر.[6][7][8]

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التطوير والتاريخ

 
 
Top and bottom views of a 2.5-inch 100 GB SATA 3.0 (6 Gbit/s) model of the Intel DC S3700 series



العمارة والوظيفة

المكونات:

  1. الذاكرة المخبئة إنگليزية: cache: محركات أقراص الحالة الصلبة تستعمل ذواكر وصول عشوائي ديناميكية كثيرة وبأحجام صغيرة كذاكرة مخبئيه، وهي شبيهة بالذاكرة المخبئية في الأقراص الصلبة.
  2. مخزن للطاقة: نوع من أنواع البطاريات، وهي ضرورية لحفظ المعلومات من الضياع في حال الانقطاع المفاجئ للتيار.

الذاكرة

ذاكرة الفلاش

مقارنة العمارة[9]
مقارنة الخصائص MLC : SLC NAND : NOR
Persistence ratio 1 : 10 1 : 10
Sequential write ratio 1 : 3 1 : 4
Sequential read ratio 1 : 1 1 : 5
Price ratio 1 : 1.3 1 : 0.7


محركات الأقراص المبنية على تقنية ذاكرة الفلاش أو محركات الأقراص الصلبة الجامدة الفلاش

أغلب مصنعي محركات الأقراص الصلبة يستخدمون تقنية ذاكرة الفلاش لصناعة محركات أقراص قوية وقابلة لتحمل الصدمات. محركات الأقراص الصلبة الفلاش لا تحتاج إلى بطاريات من أجل حفظ المعلومات، وتكون بأحجام مختلفة 3.5 و2.5 و1.8 بوصة. محركات الأقراص الصلبة الفلاش تحتفظ بالمعلومات حتى لو حصل انقطاع مفاجئ للتيار الكهربائي. وهي أبطء من ذاكرة الوصول العشوائي والقرص الصلب، ولكن قد تكون ذو أداء أفضل من الأقراص الصلبة، لأنه تم إزالة وقت البحث الذي ينتج عنه تحرك القرص وتحرك رأس القراءة والكتابة في القرص الصلب لعدم وجود أجزاء متحركة في الذاكرة.

محركات الأقراص الهجينة

الواجهة المضيفة

 
An SSD with 1.2 TB of MLC NAND, using PCI Express as the host interface[10]


التكوينات

 
A 2 GB disk-on-a-module with PATA interface

  • Viking Technology SATA Cube and AMP SATA Bridge multi-layer SSDs

  • Viking Technology SATADIMM based SSD

  • MO-297 SATA disk-on-a-module (DOM) SSD form factor

  • A custom-connector SATA SSD


المقارنة بالتقنيات الأخرى

الميزات

  • إقلاع النظام أسرع لعدم وجود أجزاء متحركة في محركات أقراص الحالة الصلبة.
  • أسرع في الوصول العشوائي للقراءة حيث لا يوجد رأس قراءة أو كتابة.
  • لا تصدر صوت لعدم وجود الأجزاء المتحركة أو عدم وجود مراوح تبريد في محركات الأقرارص صغيرة السعة (يوجد مراوح في محركات الأقراص ذات السعة العالية).
  • تستخدم تيار كهربائي أقل من القرص الصلب.
  • مستويات تحمل أعلى لدرجات الحرارة فالقرص الصلب يعمل ما بين 5-55 درجة مئوية أما محركات أقراص الحالة الصلبة فتصل مستوى تحملها إلى 70 درجة مئوية، وبعضها يصل إلى مستويات أعلى من ذلك.

العيوب

  • السعر: في منتصف 2013 كان سعر الجيجابايت لمحركات أقراص الحالة الصلبة أعلى إلى حد كبير من الجيجابايت للقرص الصلب: فكان الجيجابايت سعرة ما بين 1.00-30.45 $ دولار أمريكي للجيجابايت لمحركات أقراص الحالة الصلبة أما القرص الصلب سعر الجيجابايت تقريباً 0.038 $ دولار أمريكي.
  • المساحة: متوسط مساحة القرص الصلب أكبر بكثير من مساحة محركات أقراص الحالة الصلبة، حيث مساحة الأقراص الصلبة من الممكن أن تصل إلى 2 تيرابايت (2014)، أما محركات أقراص الحالة الصلبة فحوالي 120 جيجابايت إلى 1 تيرابايت (2014) .
  • عمر محركات أقراص الحالة الصلبة (SSD) مرتبط بعدد مرات عمليات الكتابة، فسواقة الحالة الصلبة محدودة في عمليات الكتابة مثل "فلاشة USB" ، لهذا القرص الصلب ممكن يعمل لمدة أكبر لأن عمليات الكتابة لا تؤثر فيه، لكن حدود مرات الكتابة ليس بعدد صغير.

محركات الأقراص الصلبة

 
SSD benchmark, showing about 230 MB/s reading speed (blue), 210 MB/s writing speed (red) and about 0.1 ms seek time (green), all independent from the accessed disk location.


Comparison of NAND-based SSD and HDD
Attribute or characteristic محرك أقراص الحالة الصلبة محرك الأقراص الصلبة
Reliability on storage retention If left without power, worn out SSDs typically start to lose data after about one to two years in storage, depending on temperature. New drives are supposed to retain data for about ten years.[5] MLC and TLC based devices tend to lose data earlier than SLC-based devices. SSDs are not suited for archival use. If kept in a dry environment at low temperature, HDDs can retain their data for a very long period of time even without power. However, the mechanical parts tend to become clotted over time and the drive fails to spin up after a few years in storage.
Start-up time Almost instantaneous; no mechanical components to prepare. May need a few milliseconds to come out of an automatic power-saving mode. Drive spin-up may take several seconds. A system with many drives may need to stagger spin-up to limit peak power drawn, which is briefly high when an HDD is first started.[11]
Sequential access performance In consumer products the maximum transfer rate typically ranges from about 200 MB/s to 2500 MB/s, depending on the drive. Enterprise market offers devices with multi-gigabyte per second throughput. Once the head is positioned, when reading or writing a continuous track, a modern HDD can transfer data at about 200 MB/s. Data transfer rate depends also upon rotational speed, which can range from 3,600 to 15,000 rpm[12] and also upon the track (reading from the outer tracks is faster).
Random access performance[13] Random access time typically under 0.1 ms.[14][15] As data can be retrieved directly from various locations of the flash memory, access time is usually not a big performance bottleneck. Read performance does not change based on where data is stored. In applications where hard disk drive seeks are the limiting factor, this results in faster boot and application launch times (see Amdahl's law).[16][11]

SSD technology can deliver rather consistent read/write speed, but when lots of individual smaller blocks are accessed, performance is reduced. SSDs suffer from a write performance degradation phenomenon called write amplification, where the NAND cells show a measurable drop in performance, and will continue degrading throughout the life of the SSD.[17] A technique called wear leveling is implemented to mitigate this effect, but due to the nature of the NAND chips, the drive will inevitably degrade at a noticeable rate.[التحقق مطلوب]

Read latency time is much higher than SSDs.[18] Random access time ranges from 2.9 (high end server drive) to 12 ms (laptop HDD) due to the need to move the heads and wait for the data to rotate under the magnetic head.[19] Read time is different for every different seek, since the location of the data and the location of the head are likely different. If data from different areas of the platter must be accessed, as with fragmented files, response times will be increased by the need to seek each fragment.[20]
Impacts of file system fragmentation There is limited benefit to reading data sequentially (beyond typical FS block sizes, say 4 KB), making fragmentation negligible for SSDs. Defragmentation would cause wear by making additional writes of the NAND flash cells, which have a limited cycle life.[21][22] However, even on SSDs there is a practical limit on how much fragmentation certain file systems can sustain; once that limit is reached, subsequent file allocations fail.[23] Consequently, defragmentation may still be necessary, although to a lesser degree.[23] Some file systems, like NTFS, become fragmented over time if frequently written; periodic defragmentation is required to maintain optimum performance.[24] This usually is not an issue in modern file systems.
Noise (acoustic)[25] SSDs have no moving parts and therefore are basically silent, although on some SSDs, high pitch noise from the high voltage generator (for erasing blocks) may occur. HDDs have moving parts (heads, actuator, and spindle motor) and make characteristic sounds of whirring and clicking; noise levels vary between models, but can be significant (while often much lower than the sound from the cooling fans). Laptop hard drives are relatively quiet.
Temperature control[26] A study conducted by Facebook found a consistent failure rate at temperatures between 30 and 40 °C. Failure rate rises when operating at temperatures higher than 40 °C, further increase of temperature may trigger thermal throttling around 70 °C, resulting reduced runtime performance. Reliability of early SSDs without thermal throttling are more affected by temperature, than newer ones with thermal throttling.[27] In practice, SSDs usually do not require any special cooling and can tolerate higher temperatures than HDDs. High-end enterprise models installed as add-on cards or 2.5-inch bay devices may ship with heat sinks to dissipate generated heat, requiring certain volumes of airflow to operate.[28] Ambient temperatures above 35 °C (95 °F) can shorten the life of a hard disk, and reliability will be compromised at drive temperatures above 55 °C (131 °F). Fan cooling may be required if temperatures would otherwise exceed these values.[29] In practice, modern HDDs may be used with no special arrangements for cooling.
Lowest operating temperature[30] SSDs can operate at −55 °C (−67 °F). Most modern HDDs can operate at 0 °C (32 °F).
Highest altitude when operating[31] SSDs have no issues on this.[32] HDDs can operate safely at an altitude of at most 3,000 meters (10,000 ft). HDDs will fail to operate at altitudes above 12,000 meters (40,000 ft).[33] With the introduction of helium-filled[بحاجة لمصدر] (sealed) HDDs, this is expected to be less of an issue.
Moving from a cold environment to a warmer environment SSDs have no issues on this.[بحاجة لمصدر] A certain amount of acclimation time is needed when moving HDDs from a cold environment to a warmer environment prior to operating it; otherwise, internal condensation will occur and operating it immediately will result in damage to its internal components.[34]
Breather hole SSDs do not require a breather hole. Most modern HDDs require a breather hole in order for it to function properly.[33] Helium-filled devices do not have a hole.
Susceptibility to environmental factors[16][35][36] No moving parts, very resistant to shock, vibration, and movement. Heads floating above rapidly rotating platters are susceptible to shock, vibration, and movement.
Installation and mounting Not sensitive to orientation, vibration, or shock. Usually no exposed circuitry. Circuitry may be exposed in a card form device and it must not be short-circuited by conductive materials. Circuitry may be exposed, and it must not be short-circuited by conductive materials (such as the metal chassis of a computer). Should be mounted to protect against vibration and shock. Some HDDs should not be installed in a tilted position.[37]
Susceptibility to magnetic fields Low impact on flash memory, but an electromagnetic pulse will damage any electrical system, especially integrated circuits. In general, magnets or magnetic surges may result in data corruption or mechanical damage to the drive internals. Drive's metal case provides a low level of shielding to the magnetic platters.[38][39][40]
Weight and size[35] SSDs, essentially semiconductor memory devices mounted on a circuit board, are small and lightweight. They often follow the same form factors as HDDs (2.5-inch or 1.8-inch), but the enclosures are made mostly of plastic. HDDs are generally heavier than SSDs, as the enclosures are made mostly of metal, and they contain heavy objects such as motors and large magnets. 3.5-inch drives typically weigh around 700 grams.
Reliability and lifetime SSDs have no moving parts to fail mechanically. Each block of a flash-based SSD can only be erased (and therefore written) a limited number of times before it fails. The controllers manage this limitation so that drives can last for many years under normal use.[41][42][43][44][45] SSDs based on DRAM do not have a limited number of writes. However the failure of a controller can make a SSD unusable. Reliability varies significantly across different SSD manufacturers and models with return rates reaching 40% for specific drives.[46] اعتبارا من 2011 leading SSDs have lower return rates than mechanical drives.[47] Many SSDs critically fail on power outages; a December 2013 survey of many SSDs found that only some of them are able to survive multiple power outages.[48][needs update?] HDDs have moving parts, and are subject to potential mechanical failures from the resulting wear and tear. The storage medium itself (magnetic platter) does not essentially degrade from read and write operations.

According to a study performed by Carnegie Mellon University for both consumer and enterprise-grade HDDs, their average failure rate is 6 years, and life expectancy is 9–11 years.[49] Leading SSDs have overtaken HDDs for reliability,[47] however the risk of a sudden, catastrophic data loss can be lower for HDDs.[50]

When stored offline (unpowered in shelf) in long term, the magnetic medium of HDD retains data significantly longer than flash memory used in SSDs.

Secure writing limitations NAND flash memory cannot be overwritten, but has to be rewritten to previously erased blocks. If a software encryption program encrypts data already on the SSD, the overwritten data is still unsecured, unencrypted, and accessible (drive-based hardware encryption does not have this problem). Also data cannot be securely erased by overwriting the original file without special "Secure Erase" procedures built into the drive.[51] HDDs can overwrite data directly on the drive in any particular sector. However, the drive's firmware may exchange damaged blocks with spare areas, so bits and pieces may still be present. Some manufacturers' HDDs fill the entire drive with zeroes, including relocated sectors, on ATA Secure Erase Enhanced Erase command.[52]
Price per capacity SSDs generally are more expensive than HDDs and expected to remain so into the next decade.[53]

SSD price as of first quarter 2018 around 30 cents (US) per gigabyte based on 4 TB models.[54]

Prices have generally declined annually and as of 2018 are expected to continue to do so.


HDD price as of first quarter 2018 around 2 to 3 cents (US) per gigabyte based on 1 TB models.[54]

Prices have generally declined annually and as of 2018 are expected to continue to do so.

Storage capacity In 2016, SSDs were available in sizes up to 60 TB,[55] but less costly, 120 to 512 GB models were more common. In 2016, HDDs of up to 14 TB[56] were available.
Read/write performance symmetry Less expensive SSDs typically have write speeds significantly lower than their read speeds. Higher performing SSDs have similar read and write speeds. HDDs generally have slightly longer (worse) seek times for writing than for reading.[57]
Free block availability and TRIM SSD write performance is significantly impacted by the availability of free, programmable blocks. Previously written data blocks no longer in use can be reclaimed by TRIM; however, even with TRIM, fewer free blocks cause slower performance.[58][59][60] HDDs are not affected by free blocks and do not benefit from TRIM.
Power consumption High performance flash-based SSDs generally require half to a third of the power of HDDs. High-performance DRAM SSDs generally require as much power as HDDs, and must be connected to power even when the rest of the system is shut down.[61][62] Emerging technologies like DevSlp can minimize power requirements of idle drives. The lowest-power HDDs (1.8-inch size) can use as little as 0.35 watts when idle.[63] 2.5-inch drives typically use 2 to 5 watts. The highest-performance 3.5-inch drives can use up to about 20 watts.
Maximum areal storage density (Terabits per square inch) 2.8[بحاجة لمصدر] 1.5[بحاجة لمصدر]


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بطاقات الذاكرة

المقالة الرئيسية: بطاقة الذاكرة
 
بطاقة فلاش مضغوطة مستخدمة في محركات أقراص الحالة الصلبة.

فشل محركات أقراص الحالة الصلبة

التطبيقات

دعم نظام الملفات لمحركات أقراص الحالة الصلبة

 
An SSD that uses NVM Express as the logical device interface, in form of a PCI Express 3.0 ×4 expansion card

منظمات المعايير

المنظمة أو اللجنة اللجنة الفرعية: الغرض
INCITS N/A Coordinates technical standards activity between ANSI in the USA and joint ISO/IEC committees worldwide
T10 INCITS SCSI
T11 INCITS FC
T13 INCITS ATA
JEDEC N/A Develops open standards and publications for the microelectronics industry
JC-64.8 JEDEC Focuses on solid-state drive standards and publications
NVMHCI N/A Provides standard software and hardware programming interfaces for nonvolatile memory subsystems
SATA-IO N/A Provides the industry with guidance and support for implementing the SATA specification
SFF Committee N/A Works on storage industry standards needing attention when not addressed by other standards committees
SNIA N/A Develops and promotes standards, technologies, and educational services in the management of information
SSSI SNIA Fosters the growth and success of solid state storage

التسويق التجاري

التوافر

 
Some Mtron solid-state drives


الجودة والأداء

المبيعات

انظر أيضاً

المصادر

  1. ^ Whittaker, Zack. "Solid-state disk prices falling, still more costly than hard disks". Between the Lines. ZDNet. Archived from the original on 2 December 2012. Retrieved 14 December 2012. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
  2. ^ أ ب "Solid State Storage 101: An introduction to Solid State Storage" (PDF). SNIA. January 2009. Archived from the original (PDF) on February 6, 2009. Retrieved 9 August 2010.
  3. ^ STEC."SSD Power Savings Render Significant Reduction to TCO Archived 2010-11-06 at WebCite." Retrieved October 25, 2010.
  4. ^ Vamsee Kasavajhala (May 2011). "SSD vs HDD Price and Performance Study, a Dell technical white paper" (PDF). Dell PowerVault Technical Marketing. Archived from the original (PDF) on 12 May 2012. Retrieved 15 June 2012. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
  5. ^ أ ب "Archived copy". Archived from the original on 2017-03-18. Retrieved 2017-11-05. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)CS1 maint: archived copy as title (link)
  6. ^ "WD shows off its first hybrid drive, the WD Black SSHD". Cnet. Archived from the original on 29 March 2013. Retrieved 26 March 2013. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
  7. ^ Patrick Schmid and Achim Roos (2012-02-08). "Momentus XT 750 GB Review: A Second-Gen Hybrid Hard Drive". Retrieved 2013-11-07.
  8. ^ Anand Lal Shimpi (2011-12-13). "Seagate 2nd Generation Momentus XT (750GB) Hybrid HDD Review". Archived from the original on 2013-11-01. Retrieved 2013-11-07. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
  9. ^ SLC and MLC Archived 2013-04-05 at the Wayback Machine SSD Festplatten. Retrieved 2013-04-10.
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