[maemo-users] question on booting from mmc

From: James Sparenberg james at linuxrebel.org
Date: Tue Jul 17 02:17:50 EEST 2007
On Saturday 14 July 2007 14:16:13 Frantisek Dufka wrote:
> James Sparenberg wrote:
> > I would think the reference here is to lifetime of cell X of the SD card.
> > Meaning here that each "block" (or whatever the correct term is) has a
> > set # of wrtie/read events.  JFFS from what I'm reading understands this
> > and as such move journal information around just enough to even out this
> > wear.
> >
> > My understanding is that jffs also takes steps to minimize the # of times
> > and amount of reads/writes it does.  ext3 however doesn't and it's
> > hitting the HDD a lot more often.  One of the reasons I'm not ext3's best
> > fan.
> jffs runs directly on raw NAND flash so it must do such things. SD cards
> however are normal block devices and my understanding is that they do
> same or similar wear levelling when writing blocks. So even if you write
> same (logical) block on sd card the write goes somewhere else with each
> write. I don't work for flash card manufacturer so I am not 100% sure on
> this but I guess there is no other sane way how to do it internally in
> the flash controller on the card. You need to handle same problems there
> (much bigger physical block in NAND chip than logical, pre-erasing
> blocks what data is written, remapping bad blocks, ...) like jffs2
> I think that flash cards are like harddisks nowadays. You no longer care
> about physical geometry and bad blocks on current hard disks, all is
> done transparently by disk controller and you simply don't know and
> can't even guess where on the disk specific block is really stored.
> > Ext2 and FAT don't do anything special.  They also don't do anything over
> > and over again in the same spot.
> I think FAT table is the spot which is written over and over againg in
> most devices using flash cards. Write caching is not common for
> removable media so it may be even updated after doing every write
> operation to file. And if manufacturers are giving long/lifetime
> warranty despite this common usage I wouldn't bother with ext2 or ext3
> which is typically mounted with write caching.

I could agree with the above if it all pans out as you say.  Perhaps then the 
only other anti-ext3 remark would fall along side the journal size.  Like 
I've said though I'm not much of a fan of ext3 at all. (Don't like gnome much 
either *grin*) I've lost to much data and time to ext3 over the last couple 
of years and I've only lost data with reiserfs and xfs when the drive itself 

Real question I can see at this point is which FS has the smallest journal and 
the fastest response on solid state media.  BTW the #1 reason I've lost data 
on ext3 systems was due to automagic fsck.  Admittedly those systems were 
primarily Fedora Core2 or RHEL3.  Ext3 may have improved since them but I'm 
still shy.


> Frantisek

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