From a forum post in raspberrypi.org[1]:

> My 16 GB SanDisk Extreme Pro 45 MB/s UHS 1 card reports an erase block size of 4 MB.

> My 8 GB Transcend SDHC Class 6 150x card reports an erase block size of 4 MB.

> My 2 GB Transcend SD 150x card reports an erase block size of 8 kB.

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From another post from StackExchange.com[2]:

> the data cannot be overwritten without being erased first and an erase block is the smallest unit that a NAND flash storage can erase. The erase block size is typically between 128 kB and 2 MB.

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According to a Micron Technical Note from 2006[3]:

> The NAND Flash device discussed in this technical note is based on a 2Gb asynchronous SLC device and its parameters (unless otherwise noted).

> The NAND Flash array is grouped into a series of blocks, which are the smallest erasable entities in a NAND Flash device.

> A NAND Flash block is 128KB. Erasing a block sets all bits to 1 (and all bytes to FFh). Programming is necessary to change erased bits from 1 to 0. The smallest entity that can be programmed is a byte.

(Note: 2 gigabits = 256 MB)

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In a more modern TLC 3D NAND chip from 2016[4]:

> Block Size 27,888K bytes

or 27.888MB

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[0]: https://www.google.com/search?q=microsd+erase+block+size

[1]: https://www.raspberrypi.org/forums/viewtopic.php?t=11258

[2]: https://raspberrypi.stackexchange.com/questions/32884/

[3]: https://www.micron.com/-/media/client/global/documents/produ...

[4]: https://www.micron.com/-/media/client/global/documents/produ...