Re: Flash Translation Layer?

[Bucky Katz <bucky%picovex.com@localhost>]

"Perry E. Metzger" <perry%piermont.com@localhost> writes:
>
> Most file systems are built on the assumption that the underlying
> hardware is not truly random access. This is not true in a flash
> memory. The design choices used for a file system in which substantial
> effort is made to accommodate the properties of spinning metal disks
> are not necessarily good when you are not dealing with a spinning
> metal disk.

I believe we are in violent agreement here.  Sorry I didn't make that
point myself.

>
>> You can go a long way without a journaling file system if you have an
>> FTL
>
> No one said anything about doing without a journaling file
> system. Journaling is clearly a good idea in this context. I was
> opining that FFS is not the right basis for such a file system if the
> target is flash.

I was trying to not discourage enthusiasm for adding journaling to FFS
without saying what you just said.

There really isn't a good match between NAND flash and any of the
existing filesystems available on *BSD. The closest would be LFS, and
LFS would take a lot of work to teach it to optimize for NAND
(ignoring whatever other problems it has.)

tmpfs is also not a good match because it assumes relatively fast
random access and makes no attempt to optimize i/o as a result.