[maemo-developers] Best format for SD ?

[From: Charles Werbick]

Hello All,

I've been using ext2 on the principle that journalling increases the
writes to the drive, in general. Internal wear levelling probably
negates that paradigm as the memory is likely to outlive the device. A
dozen years before failure? I'll have upgraded by then, unless we're
in 'I Am Legend' land...

Anyway, ext2 or ext3 both work well. I've been using, and booting to
ext2 on the external MMC (with swap also on MMC) as I'm hacking a ton,
so I don't want to fry anything non-replaceable. I figure, If I jack
out the MMC I can still boot to flash and buy a new card.

If you're worried about fault tolerance use ext3. The worst that'll
happen is your flash will last 10 years instead of 12.

Honestly, no matter what file system you use, the CPU speed and power
consumption (plus increased flash capacities) will obsolete the n8xx
series far before the flash wears out. The Intel Atom processors are
due out this spring and will kill ARM on tablets period. ARM simply
cannot compete with a Pentium III CPU at 1.5 GHz and 12 watts total
dissipation. I predict that the n900 series, should it reach
production, will run Intel and not TI silicon.  (I realize that I'm
setting myself up here should I be wrong. But Intel has increased the
speed of their CPU while decreasing cost, power consumption and size.
I don't see TI keeping up... Just my 2 cents.)

Cheers,
Charles Werbick




On Sun, Mar 30, 2008 at 3:08 PM, Andrew Daviel <advax at triumf.ca> wrote:
> 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...
>
>
>
>
>  --
>  Andrew Daviel, TRIUMF, Canada
>  Tel. +1 (604) 222-7376  (Pacific Time)
>  Network Security Manager
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