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TRIM vs Secure Erase

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#1 Alistair_1



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Posted 11 May 2013 - 12:12 PM

Hello all,

so I know questions regarding TRIM have been asked before, but I want to be able to clearly distinguish between TRIM and Secure Erase (Completely sanitizing the SSD). So, the underlying technology in an SSD is NAND Flash right? You can write a page but only erase a block in order to re-write to the same page.

Now when I delete a file, does the TRIM command automatically execute? I know that once TRIM is issued, the underlying file marked "unused" is deleted beyond recovery. Does TRIM work as some sort of secure erase? Or would issuing TRIM after every delete wear out the flash storage unnecessarily? As a follow up, is there a way to securely erase an SSD in one go? Do all SSDs support the ATA Secure Erase command?

Also, I was wondering if all of this is also applicable to eMMCs? The underlying storage is the same, so, let's say an Android device acts the same way when you delete a file (it just gets marked unused until the entire block gets erased).

I guess my main question is, does TRIM act like some sort of secure erase?



#2 jtsn



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Posted 12 May 2013 - 09:19 AM

TRIM is used to reduce flash wear and not to increase it. It spares the SSD controller from copying irrelevant data that resides in blocks, which are considered "free space" by the operating system.

Android devices use MTD drivers for internal storage, which operate on raw flash memory. The wear-leveling logic is included in the OS kernel.

#3 Bytebite



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Posted 13 May 2013 - 05:28 AM

TRIM allows to treat deleted blocks like free blocks, but the SSD decides when it is time to use the free blocks, deleting them would end up in program erase cycles, which would reduce lifetime.

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