Regiomontanus' angle maximization problem: Difference between revisions

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'''vRPM''', or '''virtual Revolutions Per Minute''', is a term for a synthetic [[benchmark (computing)|measurement of performance]] introduced by [[SanDisk]] for [[Solid-state drive|solid state drive (SSD)]] storage devices inside client [[personal computer|PCs]]. vRPM was created to give users a metric to compare SSD performance to the [[Hard disk drive|hard disk drive (HDD)]] and to other SSDs. It answers the question: "How fast would you have to spin a virtual HDD to achieve the performance of an SSD in a client PC?" It uses a language that users understand, [[RPM]] or Revolutions Per Minute, that is a defacto industry standard to measure the performance of the HDD inside PCs.


==Comparing SSD vs. HDD Input/Output Operation ==
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The performance of a storage device can be quantified as the number of [[Input/Output]] operations Per Second (IOPS) it achieves. HDD IOPS is proportional to RPM. When a system requests to read/write data randomly from/to a HDD, [[seek time]] and [[rotational latency]] are two HDD activities that significantly reduce HDD IOPS. Seek time is the time it takes to move the HDD head to the correct [[Cylinder (disk drive)|cylinder]] to begin to receive data. Rotational latency is the time it takes to rotate the HDD platter beneath the head so that the data can be read/written. Rotational latency varies based on the RPM of the HDD.
 
[[NAND flash]] is used as the [[non-volatile memory]] inside SSDs.  
It has faster random read than random write performance, since its write performance is delayed by the need to perform [[Garbage collection (computer science)|garbage collection]] to free space for writing. However, since NAND flash has no moving parts, the SSD achieves much higher IOPS than a HDD.
 
For the client PC usage model with approximately a 50:50 read/write ratio, a PC IOPS number can be calculated as follows:
 
:<math>PC IOPS (mean)=1/[0.5/SSD IOPS (Iwrite)] + [0.5/SSD IOPS (Iread)]</math>
 
Using this equation, the results for client SSD PC performance are as follows:
* 2006/7 SSD Generation: 5,000 Read IOPS; 10 Write IOPS; 20 PC IOPS
* 2008 SSD Generation: 10,000 Read IOPS; 100 Write IOPS; 200 PC IOPS
* 2009 (estimated) SSD Generation: 25,000 Read IOPS; 400 Write IOPS; 785 PC IOPS
 
==Converting SSD IOPS Rates into vRPM ==
 
The vRPM performance of an SSD can be calculated as follows:
 
:<math>vRPM=50/[0.5/SSD IOPS (Iwrite)] + [0.5/SSD IOPS (Iread)]</math>
 
where
*SSD IOPS (IWrite) is the sustained (to the SSD media) 4KB random write rate, Queue Depth=4
*SSD IOPS (IRead) is the sustained (to the SSD media) 4KB random read rate, Queue Depth=4
*50 is the product factor in the calculation
 
Using this calculation, SSD vRPM rates can be shown to be significantly better than HDD RPM rates, particularly in later generation SSDs:
* 2006/7 SSD Generation: 5,000 Read IOPS; 10 Write IOPS; 20 PC IOPS; 1000 vRPM
* 2008 SSD Generation: 10,000 Read IOPS; 100 Write IOPS; 200 PC IOPS; 10000 vRPM
* 2009 (estimated) SSD Generation: 25,000 Read IOPS; 400 Write IOPS; 785 PC IOPS; 40000 vRPM
 
==vRPM Adoption In Industry ==
 
Despite its early objectives, '''vRPM''' has not become broadly supported in the industry and indeed no longer appears on SanDisk's SSD website.<ref>{{cite web | url=http://www.sandisk.com/business-solutions/ssd/technical-expertise--metrics | title=Technical Expertise and Metrics | publisher=SanDisk Corporation | date=September 27, 2011 | accessdate=2011-09-27 }}</ref>
 
== See also ==
*[[Solid-state drive]]
*[[Hard disk drive]]
*[[Input/Output]]
 
== Notes ==
{{reflist}}
 
== References ==
*{{cite web | url=http://www.marketwatch.com/news/story/SanDisk-Introduces-ExtremeFFS-New-Flash/story.aspx?guid={6096177E-1745-4BFC-9046-AE82E62ABC1F} | title=SanDisk introduces ExtremeFFS — New flash management system for improving SSD performance and reliability | publisher=[[MarketWatch|MarketWatch (The Wall Street Journal Digital Network)]] | date=November 7, 2008<!-- 5:50 A.M. EST--> | accessdate=2008-11-07 }}
 
== External links ==
*[http://www.sandisk.com/Assets/File/pdf/oem/vRPM%20White%20Note.pdf vRPM White Note] by SanDisk
 
[[Category:Computer storage devices]]

Latest revision as of 22:56, 24 August 2014


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