On Thu, 2007-05-17 at 15:12 +0900, Dongjun Shin wrote: > The current trend of flash-based device is to hide the flash-specific details > from the host OS. The flash memory is encapsulated in a package > which contains a dedicated controller where a small piece of software (F/W or FTL) > runs and makes the storage shown as a block device to the host. Yes. These things are almost always implemented _very_ badly by the same kind of crack-smoking hobo they drag in off the streets to write BIOSen. It's bog-roll technology; if you fancy a laugh try doing some real reliability tests on them time some. Powerfail testing is a good one. This kind of thing is OK for disposable storage such as in digital cameras, where it doesn't matter that it's no more reliable than a floppy disc, but for real long-term storage it's really a bad idea. > IMHO, for a flash-optimized filesystem to be useful and widely-used, it would be better > to run on a block device and to be designed to run efficiently on top of the FTL. > (ex. log-structured filesystem on general block device) There's little point in optimising a file system _specifically_ for devices which in often aren't reliable enough to keep your data anyway. You might as well use ramfs. It's unfortunate really -- there's no _fundamental_ reason why FTL has to be done so badly; it's just that it almost always is. Direct access to the flash from Linux is _always_ going to be better in practice -- and that way you avoid the problems with dual journalling, along with the problems with the underlying FTL continuing to keep (and copy around during GC) sectors which the top-level filesystem has actually deallocated, etc. -- dwmw2 - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
