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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joerg.schill...@fokus.fraunhofer.de (work) Blog:
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