On Sep 6, 2011, at 9:01 PM, Freddie Cash wrote:
> Just curious if anyone has looked into the relationship between zpool dedupe, 
> zfs zend dedupe, memory use, and network throughput.


> For example, does 'zfs send -D' use the same DDT as the pool?


> Or does it require more memory for it's own DDT, thus impacting performance 
> of both?

Yes, no.

> If you have a deduped pool on both ends of the send, does -D make any 
> difference?

Yes, if the data is deduplicable.

> If neither pool is deduped, does -D make a difference?

Yes, if the data is deduplicable.

> We're waiting on a replacement backplane for our newest zfs-based storage 
> box, so won't be able to look into this ourselves until next week at the 
> earliest. Thought i'd check if anyone else has already done some comparisons 
> or benchmarks.

I'm not aware of any benchmarks, and I'd be surprised if they could be applied 
to real-world
cases. zfs send deduplication is very, very, very dependent on the data being 
sent. It is also
dependent on the release, since it is broken in many OpenSolaris and derived 
builds. Fixes
have recently been submitted into the illumos source tree. Recent Nexenta 
distributions also
have the fixes.
 -- richard

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