Subject: Re: NAND flash support
To: None <email@example.com>
From: Bucky Katz <firstname.lastname@example.org>
Date: 03/13/2007 12:46:31
"Toru Nishimura" <email@example.com> writes:
> I feel hesitating being a man of "howling for full moon," though,
> I've been skeptic about FTL/journalled flash filesys
May I join you in your howl? I too am skeptic about FTL.
But my reason for asking that NetBSD design consider it is that the
commercial file systems that we use are organized around an FTL --
even though they have a file system that is optimized for NAND use.
> Then, what characterises should be pursued to invent the filesys?
> - well-defined ordered meta operation to modify filesys.
> - a distinct block reclaim strategy; blocks which are free'd away can
> be re-written only when all the blocks are exhausted. "Never re-write
> in the place."
> We have good basis for them; the former is nothing other than
> softdep, and the latter is the characteristic (ah, goal) of BSDLFS.
> Bad block avoidance can be done in ease just FAT can do.
In a former life I participated in a project to adapt LFS to NAND for
a custom OS, without an FTL. It turns out to be a lot of work. I
recommend that a custom file system tuned to NAND characteristics be
designed and would like to participate in such a design.