On Thursday 17 September 2009 22:56:08 Kumar, Venkat wrote:
> This may not be very specific to Yaffs but a generic question on Log
> structured flash file systems.
>
> Log structured file systems are designed to avoid seek latencies (In case
> of hard disks) and to handle wear-leveling in a way (in case of flash
> disks). If a flash device is handling Wear-leveling & Bad block management,
> what is the significance of a log structured flash file system? A non-log
> structured file system should be as reliable and as efficient as a log
> structure file system.
Have a read in
http://www.yaffs.net/activity/internals
Basically: flash has the problem of needing to be erased before it is
rewritten which makes in-place writing very expensive. A log structure has
two main benefits:
* We avoid in-place writing.
* We get a degree of wear levelling.
There are downsides in a log structured fs too:
* Need to do garbage collection (but that's cheaper than in place writing).
* Scanning.
-- Charles
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