[maemo-users] question on booting from mmc

From: Frantisek Dufka dufkaf at seznam.cz
Date: Fri Jul 13 10:14:09 EEST 2007
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

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?


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