Treatise on Formatting FLASH Storage Devices
wmb at laptop.org
Wed Feb 4 17:01:43 EST 2009
Benjamin M. Schwartz wrote:
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> Mitch Bradley wrote:
>> It has been my experience that USB sticks and SD cards with intact
>> factory formatting tend to last longer and run faster than ones that
>> have been reformatted with random layouts.
> This gives us Linux users a bit of a dilemma if we want to use FTL flash
> for primary storage. FAT does not provide the file access permissions,
> symlinks, hardlinks, or even case sensitivity, that we desire for most
> filesystems on unixy systems. However, FTL devices behave as a sort of
> FAT-oriented black box, full of secret proprietary firmware that loves
I think that FTLs are getting better over time, so maybe the
FAT-specific optimizations are starting to be replaced by more generic
algorithms. The rapidly growing market for FLASH-based storage is
certainly attracting lots of development dollars.
In the absence of FAT-specific optimizations, perhaps properly-aligned
ext2 layouts will work well.
Another solution is to choose high-quality devices. I've had good
results with some models from SanDisk and Transcend. But sometimes it
comes at a cost penalty - the really good SanDisk "Extreme III" SD cards
cost 2.5x the going rate for commodity cards of the same capacity. The
good cards appear to be rather more tolerant of "abuse" than the El
Cheapo's. But even with the tough ones, I think its prudent to treat
> One obvious proposal, therefore, would be to use FAT for storage,
> but wrap it with a layer that implements all our favorite POSIX stuff.
Puppy Linux does something like that, using a (FAT, ISO9660, or
whatever) file as a container for an ext2 filesystem image.
The practice is also rather common in the world of virtualization. My
primary Linux system is actually a colinux "vm" running under Windows
with the ext2 filesystem image inside an NTFS file (actually three
files, one for root, one for home, and one for miscellaneous big wads of
client-specific stuff) . That's proven itself very convenient over
time; I've transported and mixed-and-matched those filesystem images to
several different host machines. Based on that and other pleasant
experiences with VM filesystem "snapshots", I'm of the opinion that a
quiet revolution is brewing in the way that people deal with filesystems
You could treat an existing FAT filesystem as a very flexible
partitioning scheme. You can make any number of partitions, of any
size, with a hierarchical namespace, with a good collection of tools for
> This has been done before for Linux, in the guise of UMSDOS/UVFAT .
> Although that work has fallen out of date, I suspect one could
> reimplement it quickly using new linux features such as FUSE. The
> question is: would such an approach be worthwhile?
I think that the wrapped-metadata approach has largely run its course.
There used to be a lot of activity in that area, but I haven't seen much
of interest lately. I think that containerization is likely to be the
happening thing for the near term.
> - --Ben
>  http://linux.voyager.hr/umsdos/
>  http://en.wikipedia.org/wiki/UMSDOS
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