which file system for sd card?

Chris Samuel chris at csamuel.org
Mon Jan 26 00:20:39 CET 2009

On Mon, 26 Jan 2009 3:56:26 am Pietro "m0nt0" Montorfano wrote:

> My point is: journal could avoid errors and prevent some corruption, ok
> nothing to say about that.

Journals are really to allow the filesystem to present a consistent view after 
a crash or failure and to try and avoid lengthy fsck's and the guesswork that 
is entailed in them.

So for ext3 the default behaviour is to only flush the journalled metadata of 
files after the file data has hit disk (hence why its' called "ordered" mode).  
Other filesystems make different guarantees about journals and file data (and 
so will ext3 if you mount with journal=writeback).

Regarding journal corruption - yes it can be an issue which is why ext4 (no 
longer marked experimental in 2.6.28) checksums the journal.

Filesystems like btrfs (merged as very experimental for 2.6.29) take a 
different approach, they are copy-on-write and so write new data blocks out to 
different areas of the filesystem and then update the metadata to replace the 
old with the new so you (should) have atomic updates and hence avoid the need 
for journalling.  Btrfs itself also checksums the data on disk so it will know 
if data is corrupted and (if you have two partitions in a RAID1 arrangement) 
will attempt to recover the data from the other partition (and yes, that does 

 Chris Samuel  :  http://www.csamuel.org/  :  Melbourne, VIC

This email may come with a PGP signature as a file. Do not panic.
For more info see: http://en.wikipedia.org/wiki/OpenPGP

-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 481 bytes
Desc: This is a digitally signed message part.
Url : http://lists.openmoko.org/pipermail/community/attachments/20090126/80c7d762/attachment.pgp 

More information about the community mailing list