2017-02-09 12:03 GMT+01:00 Julie Marchant <onpon4@riseup.net>:
On 02/09/17 01:50, Luke Kenneth Casson Leighton wrote:
  do you know the mkfs.ext4 commands needed or the ext2flags command?

 No, but just using an ext2 filesystem instead should suffice (since ext2 doesn't support journaling). That's the standard advice for the OpenPandora.

As we all have established. We have flash memory. Which comes in a few flavors. NAND (Not AND) and NOR (Not Or). Which is the type of logic gate used. 

Then we have SLC (Single level), MLC (Multi level) (And TLC, QLC)

With MLC, TLC, QLC you read/write multiple bits at once.
These come with an issue:
https://en.wikipedia.org/wiki/Solid-state_drive#Battery_or_supercapacitor

Then we have wear leveling. With bare Flash you have none. With SD/MCC/eMMC and SSD you have some. This is done via hardware/firmware. This is useally done in a way that is support regular rotating disk filesystem. 

The mechanics are though obscure and those controller usually are programmed by closed firmware.

So for bare NAND you should not use a regular filesystem like EXT, XFS, FAT, NTFS, etc. Also F2FS is not build for bare nand. It is made for controlled flash.

For bare NAND you should use special drivers and filesystems like MTD and UBIFS or YaFFS.
http://linux-sunxi.org/NAND

The Allwinner 3.4 kernel contains a NAND driver. But I don't know what the quality of it is. I though that I read it was not that great and that the new mainline driver had a lot of hoops to go trough to support flash formatted/controlled by the 3.4 driver.

So MLC has problems with power loss. So a journalling filesystem is a must. A journalling FS has noting to do with logging. But with write consistency.

With (e)MMC/SD adn SSD you lose a bit of freedom and gain extra security issues. But makes programming easier.

So weather NAND suffers from wear or age: You need a good controller (hardware or software) identifying broken cells and marking them unfit and not bother progams or users with unwritable sectors.


 


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