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 Post subject: Crucial MX500 Write Amplification Factor
PostPosted: March 25th, 2020, 17:14 
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Joined: September 8th, 2009, 18:21
Posts: 12689
Location: Australia
Here is an interesting (and very long) thread where a user has experienced a huge Write Amplification Factor (WAF) in a Crucial MX500 SSD:

https://forums.tomshardware.com/threads/crucial-mx500-500gb-sata-ssd-remaining-life-decreasing-fast-despite-few-bytes-being-written.3571220

The workaround was to implement a background CMD batch script which repeatedly executed a SMART self test (smartctl) punctuated by 20 minute waits:

https://forums.tomshardware.com/threads/can-a-series-of-smart-selftests-be-made-to-span-the-entire-ssd-if-each-selftest-is-periodically-aborted.3581869

Can anyone suggest how and why this workaround was able to tame the astronomical WAF?

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 Post subject: Re: Crucial MX500 Write Amplification Factor
PostPosted: April 10th, 2020, 3:21 
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Joined: August 13th, 2016, 17:10
Posts: 103
Location: Vienna, Austria
Yes, from my point of view, there is a lot of things going on inside a SSD that is causing program writes to the NAND flash that is completely unrelated to Host Writes. E.g. For SMART, the SSD has to collect various data and regularly write that data to the disk. It has to calculate the power-on-hours, it has to measure temperature, it needs to backup the FTL and various other configuration status, ... the SSDs are logging a lot of stuff regularly in the SA. And not all of those writes are necessarily optimized for a WAF. Now usually (Data-Center, normal Desktop users) that isn't much compared to the Host-Writes. But in this scenario the user explicitly said that he isn't using the disk very much. So all those internal processes are likely far more in this scenario than normally, which accounts to an astronomic WAF. You can think of an SSD/HDD like a small computer inside the case of the SSD. And that computer does a lot of stuff, and therefore uses the NAND flash a lot.
One thing for example is that SSDs are running background tasks like e.g. scanning for bad blocks and remapping them. There are no host writes for that, it's only running when the SSD is idle. So any regularly triggered SMART actions can likely stop those background tasks from running. I am not sure, whether holding off the SSD from doing those background tasks is a good idea. It could be, but it could also cause bigger troubles. -> Backup, backup, backup!


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