On Fri, May 27, 2011 at 07:28:06AM -0400, Edward Ned Harvey wrote: > > From: Daniel Carosone [mailto:d...@geek.com.au] > > Sent: Thursday, May 26, 2011 8:19 PM > > > > Once your data is dedup'ed, by whatever means, access to it is the > > same. You need enough memory+l2arc to indirect references via > > DDT. > > I don't think this is true.
> The reason you need arc+l2arc to store your DDT > is because when you perform a write, the system will need to check and see > if that block is a duplicate of an already existing block. If you dedup > once, and later disable dedup, the system won't bother checking to see if > there are duplicate blocks anymore. So the DDT won't need to be in > arc+l2arc. I should say "shouldn't." dedup'd blocks are found via the ddt, no matter how many references to them exist. The ddt 'owns' the actual data block, and the regular referencing files' metadata (bp) indicates that this block is dedup'd (indirect) rather than regular (direct). At least that's my somewhat-rusty recollection. -- Dan.
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