[Soekris] "Squashed" versions of FreeBSD

[Joel Jaeggli]

Brian W. Antoine wrote:
>> I may be wrong, but I didn't think the failure mode would be
>> a "sudden and unexpected" downtime. I had assumed I'd start to
>> see read/write errors like you see when a HDD slowly gets
>> bad sectors. However, rethinking that, I'm not sure what to
>> expect.
> 
> It depends on the filesystem.  The Flash FileSystem might be smart
> enough to remap blocks on the fly when a read-after-write validation
> fails, or it might simply be erasing and rewriting the same block
> until it fails.  In that case you'll either loose a file or your
> filesystem, depending on whether it was a data or inode block that
> went bad.

There's been a lot of work done by ssd manufacturers that bleeds over 
into cf cards (which use the same chipsets) to implement these features 
in the controller... The result is:

1. you can use your normal filesystem

2. you flash specific filesystem optimizations may work at cross
    purposes to a controller firmware implementation that's been designed
    to support a windows vista pagefile on ntfs on flash media.

> Those cells can only be written to zero just so many times.  These
> days it's a much larger number of times, but the limit still exists.

The bigger the media the more cells there are for the wear leveling 
algorythm to work across... you can write continously to an 8GB flash 
card at 30MB/s (about the fastest you can buy when you factor in the 
erase cycle) for .84 years before you hit 100,000 cycles.

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