Write amplification: differenze tra le versioni

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The second source of over-provisioning comes from the manufacturer, typically at 0%, 7% or 28%, based on the difference between the decimal gigabyte of the physical capacity and the decimal gigabyte of the available space to the user. As an example, a manufacturer might publish a specification for their SSD at 100, 120 or 128&nbsp;GB based on 128&nbsp;GB of possible capacity. This difference is 28%, 7% and 0% respectively and is the basis for the manufacturer claiming they have 28% of over-provisioning on their drive. This does not count the additional 7.37% of capacity available from the difference between the decimal and binary gigabyte.<ref name="Jim_Bagley" /><ref name="Smith_2012" />

The third source of over-provisioning comes from known free space on the drive, gaining endurance and performance at the expense of reporting unused portions, and/or at the expense of current or future capacity. This free space can be identified by the operating system using the TRIM command. Alternately, some SSDs provide a utility that permit the end user to select additional over-provisioning. Furthermore, if any SSD is set up with an overall partitioning layout smaller than 100% of the available space, that unpartitioned space will be automatically used by the SSD as over-provisioning as well.<ref name="Smith_2012" /> Yet another source of over-provisioning is operating system minimum free space limits; some operating systems maintain a certain minimum free space per drive, particularly on the boot or main drive. If this additional space can be identified by the SSD, perhaps through continuous usage of the TRIM command, then this acts as semi-permanent over-provisioning. Over-provisioning often takes away from user capacity, either temporarily or permanently, but it gives back reduced write amplification, increased endurance, and increased performance.<ref name="Layton" /><ref name="Drossel" /><ref name="Anand_Spare_Area">{{cite web |url=http://www.anandtech.com/show/3690/the-impact-of-spare-area-on-sandforce-more-capacity-at-no-performance-loss |title=The Impact of Spare Area on SandForce, More Capacity At No Performance Loss? |page=2 |author=Shimpi, Anand Lal |publisher=AnandTech.com |date=3 maggio 2010 |accessdate=19 giugno 2010}}</ref><ref>{{cite web | url=http://www.storagereview.com/intel_ssd_520_enterprise_review |title=Intel SSD 520 Enterprise Review |quote=20% over-provisioning adds substantial performance in all profiles with write activity| first=Kevin|last= OBrien | work= Storage Review | date = 6 febbraio 2012 | accessdate=29 novembre 2012 }}</ref><ref>{{cite web | url=http://cache-www.intel.com/cd/00/00/45/95/459555_459555.pdf | archiveurl=https://web.archive.org/web/20111125012226/http://cache-www.intel.com/cd/00/00/45/95/459555_459555.pdf | archivedate=25 novembre 2011 | title=White Paper: Over-Provisioning an Intel SSD | publisher=Intel | format=PDF | year=2010 | accessdate=29 novembre 2012 | urlmorto=yessì }}</ref>

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