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Date: Mon, 31 Mar 2008 21:53:47 -0700
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Thread-Topic: Flash disks and FFS layout heuristics
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From: "Martin Fouts" <mfouts@danger.com>
To: "Matthew Dillon" <dillon@apollo.backplane.com>
Cc: Christopher Arnold <chris@arnold.se>, arch@freebsd.org, qpadla@gmail.com,
	freebsd-arch@freebsd.org
Subject: RE: Flash disks and FFS layout heuristics
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=20

> -----Original Message-----
> From: Matthew Dillon [mailto:dillon@apollo.backplane.com]=20
> Sent: Monday, March 31, 2008 3:54 PM
> To: Martin Fouts
> Cc: qpadla@gmail.com; freebsd-arch@freebsd.org; Christopher=20
> Arnold; arch@freebsd.org
> Subject: RE: Flash disks and FFS layout heuristics
>
> If I were reimplementing HAMMER as a flash filesystem=20
> (which I am NOT doing), I would probably do away
> with the blockmap layer entirely since seek locality of=20
> 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.