<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
<HTML>
<HEAD>
<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1">
<META NAME="Generator" CONTENT="MS Exchange Server version 5.5.2448.0">
<TITLE>"FS over BLOCKDEV over FLASH" versus "FS over FLASH"</TITLE>
</HEAD>
<BODY>
<P><FONT SIZE=2>Hello,</FONT>
<BR> <FONT SIZE=2>There are two posibilities for implementing a filesystem over a flash device (DiskOnChip or others).</FONT>
<BR> <FONT SIZE=2>One, is implementing a block device emulation layer over flash, and then a filesystem over it. The block device emulation layer can be a wear leveliong one (like M'Systems NFTL) or one that just maps flash memory like linear contiguous sectors. The filesystem over the block device needs to have a journal or to be log structured to be inmune to power failures and crashes.</FONT></P>
<P> <FONT SIZE=2>The other apporoach, is implementing a filesystem over flash directly.</FONT>
<BR> <FONT SIZE=2>What I don´t understand, is what is the difference between layering the filesystem over the block device and directly over flash ? The "block device" layer, isn´t just an abstraction for some REAL device that adapts well to the concept of contiguous sectors? Doesn´t flash memory adapt to that concept?</FONT></P>
<P> <FONT SIZE=2>What are the drawbacks of implementing a standard log structured filesystem over a block device abstraction of the flash that doesn´t implement wear leveling?</FONT></P>
<BR>
<P><FONT SIZE=2>Diego Roig Seigneur</FONT>
<BR><FONT SIZE=2>Gerencia de Desarrollo</FONT>
<BR><FONT SIZE=2>Research & Development</FONT>
<BR><FONT SIZE=2>Clave Electrónica SA</FONT>
<BR><FONT SIZE=2> </FONT>
<BR><FONT SIZE=2>Mail Address:</FONT>
<BR><FONT SIZE=2>Salguero 2493</FONT>
<BR><FONT SIZE=2>(B1650BTG) San Martín</FONT>
<BR><FONT SIZE=2>Argentina</FONT>
<BR><FONT SIZE=2>Tel: +54-11-4755-4554</FONT>
<BR><FONT SIZE=2>Fax: +54-11-4753-3265</FONT>
<BR><FONT SIZE=2><A HREF="mailto:diego.roig@grupoclave.com">mailto:diego.roig@grupoclave.com</A></FONT>
<BR><FONT SIZE=2><A HREF="http://www.grupoclave.com" TARGET="_blank">http://www.grupoclave.com</A></FONT>
</P>
</BODY>
</HTML>