zeroing out part of an SDcard

[Chris Murphy]

SD Specifications
Part 1
Physical Layer
Simplified Specification
Version 4.10
https://www.sdcard.org/downloads/pls/simplified_specs/part1_410.pdf

page 38

4.3.5 Erase
It is desirable to erase many write blocks simultaneously in order to enhance the data throughput. Identification of these write blocks is accomplished with the ERASE_WR_BLK_START (CMD32), ERASE_WR_BLK_END (CMD33) commands. 
The host should adhere to the following command sequence: ERASE_WR_BLK_START, ERASE_WR_BLK_END and ERASE (CMD38).


So there's something like trim, but trim is an ATA command. But I don't know whether this is what mkfs.btrfs is using, or if it's asking some other library to do it, and it's that library that differentiates and mkfs.btrfs has no idea. And then whether fstrim is using some other library and hence the difference.

Rabbit hole.


Chris Murphy