Flash disks and FFS layout heuristics

[Martin Fouts]

> -----Original Message-----
> From: Matthew Dillon [mailto:dillon at apollo.backplane.com] 
> Sent: Tuesday, April 01, 2008 1:10 PM
> To: Martin Fouts
> Cc: freebsd-arch at freebsd.org
> Subject: RE: Flash disks and FFS layout heuristics
> 
>     64MB is tiny.  None of the problems with any of the 
> approachs we've discussed even exist with devices that small in an 
> embedded system.

It is fairly clear that you're not familiar with NAND devices on
embedded systems, as you've just said that well known problems do not
exist.

> To be clear, because I really don't understand how you 
> can possibly argue that the named-block storage layer is bad in a 
> device that small...

Yes, your lack of understanding is very apparent.

> It's seriously a non-issue.  You are making too many 
> assumptions about how named blocks would be used, particularly
> if the filesystem is flash-aware.

Now you're moving your goal posts. You came into this suggesting that
the file system not be flash-aware. If I make the file system flash
aware than many of the problems become managable.  That *was* my
starting thesis, after all.

> Now, if you want to argue that this model would have 
> serious performance penalities please go ahead,
> I'm all ears.

Feel free to implement it and see for yourself.

The only point I had wished to make is that you get performance wins out
of making the file system flash aware. Now that you've agreed to that,
feel free to experiment with any of a number of ways of making it flash
aware.