Bob Friesenhahn <bfrie...@simple.dallas.tx.us> wrote:

> Yes of course.  Properly built SSDs include considerable extra space 
> to support wear leveling, and this same space may be used to store 
> erased blocks.  A block which is "overwritten" can simply be written 
> to a block allocated from the extra free pool, and the existing block 
> can be re-assigned to the free pool and scheduled for erasure.  This 
> is a fairly simple recirculating algorithm which just happens to 
> also assist with wear management.

I believe you make a mistake with this assumption.

-       The SSD cannot know which blocks are currently not in use.

-       In special with a COW filesystem, after some time all net space
        may have been written to but the SSD does not know whether it
        is still used or not. So you see s mainly empty filesystem
        while the SSD does not know this fact.

-       If wou write not too much to a SSD, it may be that the spare space
        for defect management is sufficient in order to have suficient
        prepared erased space.

-       Once you write more, I see no reason why a COW filesystem should
        be any better than a non-COW filesystem.


        
        Jörg

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