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SubjectRe: mode data=journal in ext3. Is it safe to use?
Ken Ryan wrote:

> Hans Reiser wrote:
>
>> Timothy Miller wrote:
>>
>>> Doesn't Reiser4 do wear-leveling for flash?
>>
>>
>>
>> No, we don't. We do have wandering logs, so it would be feasible to
>> code, but bitmap blocks and super blocks get written to the same
>> locations repeatedly.
>>
>> Actually, most compact flash devices DO do wear leveling, from what I
>> have heard.
>
>
>
> The ones I've seen, only sort of. They'll allocate writes from
> available erased pages to try to distribute their use, but if you
> have a disk that's, say, 70% read-only data and 30% read-write then
> the wear-levelling will only happen on that
> 30% of the disk. True wear levelling will actually scrub read-only or
> rarely-written data, forcing it to get off its
> duff so the flash cells they're sitting on can get some exercise, and
> give the more worn cells a rest (that scrub
> helps ECC fix soft errors from weak cells too). True wear-levelling
> is really hard, and obviously requires
> budgeting extra bandwidth and storage devices for safely shuffling
> around data that the application has no
> intention of moving (picture losing power in the middle of a scrub).
> It's not worth it for the consumer CF
> usage model of "take photos until the card is full, then copy them all
> to the PC and wipe the card clean".
>
> [Yes, I tend to see this from the inside-out: I'm actually an
> FPGA/ASIC weenie not a kernel hacker. One of my current
> projects is part of a controller chip for a solid-state storage system
> with ${bignum} NAND flash chips. Alas, my specialty
> is video and graphics, so I'm still coming up the learning curve on
> storage systems].
>
> ken
>
>
>
>
>
Interesting. Thanks for educating me.

No existing general purpose filesystem that I know of will address your
needs. We could of course write one if someone paid for it....
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