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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