[Lazarus] Using Lazarus on Embedded Linux?
mschnell at lumino.de
Wed Sep 29 12:26:21 CEST 2010
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.
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