Flash disks and FFS layout heuristics

[Martin Fouts]

> -----Original Message-----
> From: Matthew Dillon [mailto:dillon at apollo.backplane.com] 
> Sent: Monday, March 31, 2008 3:54 PM
> To: Martin Fouts
> Cc: qpadla at gmail.com; freebsd-arch at freebsd.org; Christopher 
> Arnold; arch at freebsd.org
> Subject: RE: Flash disks and FFS layout heuristics
>
> If I were reimplementing HAMMER as a flash filesystem 
> (which I am NOT doing), I would probably do away
> with the blockmap layer entirely since seek locality of 
> reference is not needed for a flash filesystem, and the global
> B-Tree would serve directly as the named-block topology.

Which would lead you almost directly to the sort of performance problems
that jffs2 has.

Until you've done it, you'll be surprised at the cost of maintaining
b-trees in NAND.