[maemo-users] question on booting from mmc

From: James Sparenberg james at linuxrebel.org
Date: Sat Jul 14 23:19:53 EEST 2007
On Friday 13 July 2007 00:14:09 Frantisek Dufka wrote:
> Theodore Tso wrote:
> > Yeah, but the ext3 journal wears out the flash card much more quickly.
> Since you know better than anyone how ext3 works can you quantify what
> means 'much more quickly' with default date=ordered mode? 2x 10x 100x ?
> My only information is from
> http://www.redhat.com/support/wpapers/redhat/ext3/

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.    Given 
this you have even more of the reason jffs was invented.  If all that was 
needed was compression cramfs would be used more often as it does compress 
greater and is supposedly more mature.  

Ext2 and FAT don't do anything special.  They also don't do anything over and 
over again in the same spot.  So FAT is a compromise in that "everyone can 
read FAT" since that FS is long since reverse engineered.  EXT2 is the linux 
equal to FAT Older.  Solid and  a fallback that always works.  

My only Question with ext2 is.... can it do a partition larger than 2GB 
effectively, as for a long time this was one of it's big limits.  


> Also I suppose the basic IT200x system is somewhat optimized for writes
> so typically the amount of data written is not exactly huge. We are also
> mounting mmc with 'noatime'.
> > Given how cheap 2GB cards are, maybe we don't care
> Yes, they are cheap and I guess internal wear levelling should be pretty
> good to allow 'lifetime' guarantee with FAT filesystem.
> Check also (end of) https://bugs.maemo.org/show_bug.cgi?id=598
> Also cards are getting bigger quickly so most people are not using the
> card for long (like >3 years) but upgrade to bigger cards.
> > but given how
> > quick e2fsck is on a 2GB flash disk, another approach would be modify
> > the boot script so that it detects if the root filesystem is ext2, and
> > if it is unclean, force an fsck automatically.
> This is slightly problematic. There is no fsck in initfs partition and
> space is really tight there. Also we have no keyboard so realistically
> -y is the only option which may sometimes do something wrong. From the
> manpage: ...  Sometimes an  expert  may  be  able to do better driving
> the fsck manually. ... AUTHOR Theodore Tso
> Anyway, isn't mount with data=writeback (and possibly also commit=30)
> same or better for data integrity (or in kernel fsck chance to do right
> thing at boot time) than pure ext2 with e2fsck?
> Frantisek
> _______________________________________________
> maemo-users mailing list
> maemo-users at maemo.org
> https://lists.maemo.org/mailman/listinfo/maemo-users

More information about the maemo-users mailing list