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→Appendix 2: Video
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|{{oldid|16652|3.0.0}}
|May 2022
|Added detailed analysis of e.MMC accesses (SanDisk SDINBDG4-8G-XI1)
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|Added video of technical presentation by Lauterbach Italy
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Another extremely useful graphical depiction is the chunk size distribution. For instance, this information is often used to understand how efficient the user application is when it comes to optimize the write operations for maximizing the e.MMC lifetime. The pie on the left refers to the read operations, while the other one refers to the write operations.
[[File:MISC-TN-017-eMMC-chart2-chunk-size.png|center|thumb|800x800px|Chunk size distribution]]
To interpret the result, one needs to take into account how the workload was implemented. In the example under discussion, the workload basically makes use of two applications: <code>[https://man7.org/linux/man-pages/man1/dd.1.html dd]</code> and <code>stressapptest</code>. <code>dd</code> was specified to use 4-kByte data chunks (<code>bs=4k</code>). <code>stressapptest</code> uses 512-byte chunks instead because the <code>--write-block-size</code> parameter was not used (for more details please refer to the [https://github.com/stressapptest/stressapptest/blob/e6c56d20c0fd16b07130d6e628d0dd6dcf1fe162/src/worker.cc#L2615 source code]). As a result, one would expect that the majority of accesses are 512 bytes and 4 kByte. The charts clearly show that this is not the case. Most of the accesses are 512kB instead. This is a blatant example of how the algorithms of the file systems and the kernel block driver can alter the accesses issued at application levels level for optimization purposes.
==== Appendix 1: source code example ====
}
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==== Appendix 2: Video ====
Technical Note presentation by Lauterbach (Language: Italian; Subtitles: English and Italian)
{{#ev:youtube|YDWAGy2QnA0|600|center|Persistent storage and read-write file systems|frame}}
=== Device's built-in advanced functionalities ===
== Example: embedded Linux system equipped with an e.MMC ==
As explained in [[#Embedded Linux systems with eMMC or SD cards|this section]], e.MMC's provide specific functionalities for device's health monitoring. In practice, these components expose some registers that make health-related information available to the host.
The health status registers can be exploited to implement a monitoring mechanism as well. For example, a user-space application can poll periodically the status of the device and take actions accordingly if the wear-out exceeds predefined thresholds.
Last but not least, it is worth remembering that advanced proprietary off-line tools may also be available for health monitoring. For instance, Western Digital provides such tools for its devices. For more information, please contact our [mailto:sales@dave.eu Sales Department].
= References =
