[Arm-netbook] Logging and journaling

[mike.valk at gmail.com]

2017-02-09 12:03 GMT+01:00 Julie Marchant <onpon4 at 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.




>
>
> _______________________________________________
> arm-netbook mailing list arm-netbook at lists.phcomp.co.uk
> http://lists.phcomp.co.uk/mailman/listinfo/arm-netbook
> Send large attachments to arm-netbook at files.phcomp.co.uk
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.phcomp.co.uk/pipermail/arm-netbook/attachments/20170210/f0ca51c5/attachment-0001.html>