[maemo-developers] Best format for SD ?

[From: Andrew Daviel]

On Sun, 30 Mar 2008, Ryan Pavlik wrote:

>> What is the best available F/S for flash ? And what options ?
>> 
>> I saw an interesting webcast by Mentor Graphics where they were talking 
>> about designing a new filesystem especially for flash, which would be

> With regard to limited write cycles, SD cards automatically and internally do 
> wear leveling (that is, writing to place 0 on the drive might never be the 
> same place) to counter that effect, so that's why FAT works without burning 
> out cards writing the FAT every time you change something.  When you have a 
> "memory technology device" - aka, just a flash chip directly attached some 
> how, not through SD (think the internal 256), then a file system like JFFS 
> (which the Nokia devices use) does compression and wear levelling at the FS 
> level.

I was just looking at JFFS2. As you say, it's designed for direct access 
to flash rather than over SCSI emulation. When I re-read my notes on the 
Mentor talk (they are big in electronic circuit design, and would be 
providing hardware libraries for ASIC and (F)PGA design) they do mention 
JFFS and YAFFS and say that their "Mentor Safe File System" would be an 
improvement with 100% power fail safety and with various optimization for 
NOR (fast read) NAND (fast write) hybrids etc. I think NAND support was a 
relatively recent addition to JFFS2.

I'm still interested in which of the various f/s (ext2/3, xfs, jfs, 
reiser ...) might be better on SD (mounted over USB via SCSI emulation)
if I don't care about Windows compatability. Then there's the extended 
attributes (used by Apple's calendar server), not that I have immediate 
plans for that...



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Andrew Daviel, TRIUMF, Canada
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