Re: document ext3 requirements

Rob Landley
2009-01-05T02:51:49Z

On Sunday 04 January 2009 17:13:08 Sitsofe Wheeler wrote:
> Pavel Machek wrote:
> > Is there linux filesystem that can handle that? I know jffs2, but
> > that's unsuitable for stuff like USB thumb drives, right?
>
> This raises the question that if nothing can handle it which FS is the
> least bad? The last I heard people were saying that with cheap SSDs the
> recommendation was FAT [1] but in the future btrfs, nilfs and logfs
> would be better.
>
> [1] http://lkml.org/lkml/2008/10/14/129

I wonder if the flash filesystems could be told via mount options that they're
to use a normal block device as if it was a flash with granularity X?

They can't explicitly control erase, but writing to any block in a block group
will erase and rewrite the whole group so they can just do large write
transactions close to each other and the device should aggregate enough for an
erase block. (Plus don't touch anything _outside_ where you guess an erase
block to be until you've finished writing the whole block, which they
presumably already do.)

The other question is whether there's any way to guess an erase granularity
that's "good enough" for a device of size X, maybe larger than the device
actually does but not smaller than any remotely sane manufacturer would
implement. (And just _don't_ partition these suckers, so you don't have to
worry about partitions aligning with erase block sizes.)

Rob