[Sugar-devel] Filesystem for SD cards / USB sticks (was: Re: Unbootable machine)

[Sascha Silbe]

On Sun, Aug 30, 2009 at 09:33:22PM -0400, Bernie Innocenti wrote:

> On a side note, which filesystem should be chosen in order to minimize
> wearing to USB sticks?
Only the manufacturer can know. Maybe we should ask a few of them. :-|
The problem is that the FTL is highly proprietary and very likely tuned 
to the FAT filesystem (since it's the one mandated by the SD card 
standard). It's entirely possible that it makes some assumptions that 
are invalid for non-FAT and does strange things then.
This might be causing the abyssmal performance (<< 1MB/s write speed) I 
experience lately on my XO-1 (with as much structures as possible 
aligned on 4MB blocks), though having the Journal aligned only to 128KB 
blocks (ext3) might be part of the problem as well (16GB SiliconPower 
SDHC card, erase block size unknown). The initial raw write speed was up 
to 20MB/s (12MB/s on the XO-1), dropping to 4-5MB/s on the XO-1 after 
installation, now down to 500KB/s max. These figures are for sequential 
writing of large files (using dd with conv=fsync), random writes seem to 
be even worse (observed using dstat).

> I would assume that the any DOS filesystem will continouously rewrite 
> to
> the FAT blocks.  Maybe the best choice would be ext4 with the journal
> disabled?
The increase of data written to the card with journalling enabled is 
less than 4% for normal operations (up to 42% for very 
metadata-intensive operations, but then the amount written is low in 
absolute terms) according to Ted Ts'o [1] (who has quite a number of 
interesting SSD-related articles in his blog). For me having a 
journalling filesystem is worth a lot more than just 4% write data 
increase (I even use data=journal on most systems).


[1] 
http://thunk.org/tytso/blog/2009/03/01/ssds-journaling-and-noatimerelatime/

CU Sascha

-- 
http://sascha.silbe.org/
http://www.infra-silbe.de/
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