Re: Filesystem for block devices using flash storage?

[Chris Snook]

JÃrn Engel wrote:
> On Mon, 13 October 2008 13:30:29 -0400, Chris Snook wrote:
> > > > logfs tries to solve the write amplification problem by forcing all write 
> > > > activity to be sequential.  I'm not sure how mature it is.
> > > Still under development.  What exactly do you mean by the write
> > > amplification problem?
> > Write amplification is where a 512 byte write turns into a 128k write, 
> > due to erase block size.
>
> Ah, yes.  Current logfs still triggers that a bit too often.  I'm
> currently working on the format changes to avoid the amplification as
> much as possible.
>
> Another nasty side effect of this is that heuristics for wear leveling
> are always imprecise.  And wear leveling is still required for most
> devices.  See http://www.linuxconf.eu/2007/papers/Engel.pdf
>
> > Intel is claiming a write amplification factor of 1.1.  Either they're 
> > using very small erase blocks, or doing something very smart in the 
> > controller.
>
> With very small erase blocks the facter should be either 1 or 2, not
> 1.1.  Most likely they work very much like logfs does, essentially doing
> the whole log-structured thing internally.
>
> JÃrn

As I understand it, they mean that in a real-world workload that writes 1x data, 
a total of 1.1x is written on flash.  Real-world writes are usually, but not 
always, larger than a single sector.  Of course, the validity of this number 
depends greatly on the test.

If someone has more info on the Intel devices, please clue me in.

-- Chris
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