This article raises the concern that SSD controllers (in particular
SandForce) do internal dedup, and in particular that this could defeat
ditto-block style replication of critical metadata as done by
filesystems including ZFS.
http://storagemojo.com/2011/06/27/de-dup-too-much-of-good-thing/
Along with discussion of risk evaluation, it also suggests that
filesystems could vary each copy in some way (internal serial / nonce)
to defeat the mechanism.
Comments and suggestions, aside the risk evaluation piece?
This doesn''t appear to mean that zfs dedup is of no use on such
drives, since they still present the same number of externally
accessible blocks. The internal dedup evidently allows them to
maintain more spare/free sectors for g/c and performance reasons.
PS. I intend to ignore the risk discussion because in most cases zfs
users concerned aboutthese and many other related risks will mitigate
them using multiple independent devices.
--
Dan.
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