[PATCH 1/1] ubi: Introduce block devices for UBI volumes

[Richard Weinberger]

Am 09.02.2014 00:37, schrieb Willy Tarreau:
>>> I gave an example with ext2 for the config. It's a bit excessive to
>>> quickly declare "there is simply no use case for $put_your_option_here",
>>> it just means that *you* don't have this use case, which I perfectly
>>> respect.
>>
>> The mail with your ext2 use case arrived afterward I've sent that mail.
> 
> No problem.
> 
>> So you are using ext2 as config filesystem because you're facing issues with ubifs?
> 
> No, I've been using ext2 on x86-based hardware and compact flash for
> something like 10 years with a great success (easy to mount, easy to
> fix, easy to save, easy to occasionally add a backup copy or an extra
> data file, etc). I contemplated ubifs on NAND devices as an alternative
> when starting to play with ARM-based devices, and lost the reliability
> and ability to fix. Switching back to the proven ext2 completely solved
> the issues in the end. Ubifs is nice when you need a real read/write FS,
> but most small devices do not need wear leveling or any of such nice
> features. When you just write 1-10 times a year, other solutions are
> fine enough. Using mtdblock directly is not reliable because of bad
> blocks which come from time to time. If your FS happens to be located
> on one of them, you're screwed. UBI solves such issues and ubiblock
> provides a nice interface for this. I even thought about putting the
> kernel on top of UBI so that it better resists NAND issues, but some
> versions of u-boot do not seem to update it correctly.

Thanks a lot for the detailed explanation.

> In fact, my feeling is that ubiblock provides the same flexibility
> with MTD as you have on new devices with eMMC. You have no wear
> levelling, and so what ? You never know if your eMMC does it well
> either. I even had a series of compactflash which died after a small
> number of writes in the past, so that has existed and will always.
> 
> Also, all these low-level features on top of MTD are used by people
> who try to build systems and who are expected to understand a little
> bit some of the limits of the solutions they use. It's not the basic
> joe user who will install ext4 on top of ubiblock on his NAND by
> himself.

My experience has shown the opposite. ;-)

> This I think it's a bad idea to artificially remove some features
> if they're not broken.

Your arguments have convinced me, let's keep it and hope the best.

Thanks,
//richard