On 09/28/2010 11:56 AM, Henry Vermaak wrote:
No. If you have a disk that does out of order write caching, you will
have to enable barriers (which are not enabled on ext3 by default, for
example). Then you may still have the problem of some disks not
implementing the flushing correctly, at which point you will have to
disable the write caching, which will have a big performance impact.
Of course you are correct as such a disk also does "complex stuff"
inside. But a disk with a cache will never trash data that has been
written long ago. The wear leveling in a flash card needs to move such
data ()user data and it's own management blocks) around. This results in
the said effects.
My point is that you are always at the mercy of your device (not just
with sd/mmc).
Yep. But I do suppose that you can get information from the disk
manufacturers how long it might take at most to write the cache back to
the disk and I don't think this is more than some mSeks. While with
Flash cards this time can be long (supposedly max several seconds) and
the manufactures don't provide a spec of that.
A good sd/mmc will implement a log structured file system in the
translation layer that won't be prone to data loss.
An sd/mmc does not implement a file system at all.
I fear that we're very far off topic again.
yep.
-Michael
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