Flash disks and FFS layout heuristics

[Martin Fouts]

> -----Original Message-----
> From: Matthew Dillon [mailto:dillon at apollo.backplane.com] 
> Sent: Monday, March 31, 2008 1:06 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
> 
> 
>     But how do you index that information?  You can't simply 
> append the information to the NAND unless you also have a way to 
> access it.  So does the filesystem have to scan the NAND (or
significant 
> portions of it) in order to build an index of the filesystem topology
in 
> system memory?
> 
>     No matter what you do you have to index the information 
> *SOMEWHERE*.

And NAND devices have a *SOMEWHERE* that makes them different than other
persistent storage devices in ways that make them interesting to do file
systems for.

It's not _that_ you have to scan the NAND, by the way, it's _when_ you
scan the NAND that has the major impact on performance.