> From: Daniel Carosone [mailto:d...@geek.com.au]
> Sent: Wednesday, May 25, 2011 10:10 PM
> 
> These are additional
> iops that dedup creates, not ones that it substitutes for others in
> roughly equal number.

Hey ZFS developers - Of course there are many ways to possibly address these
issues.  Tweaking ARC prioritization and the like...  Has anybody considered
the possibility of making an option to always keep DDT on a specific vdev?
Presumably a nonvolatile mirror with very fast iops.  It is likely a lot of
people already have cache devices present...  Perhaps a property could be
set, which would store the DDT exclusively on that device.  Naturally there
are implications - you would need to recommend mirroring the device, which
you can't do, so maybe we're talking about slicing the cache device...  As I
said, a lot of ways to address the issue.

Both the necessity to read & write the primary storage pool...  That's very
hurtful.  And even with infinite ram, it's going to be unavoidable for
things like destroying snapshots, or anything at all you ever want to do
after a reboot.

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