Memory consumption after turning off dedup

[Daniel Kalchev]

The only way I am aware of to get rid of the DDT (what is consuming memory) is to turn dedup off, then copy all the data in again -- if you have space, you could copy within the same zpool, then remove the old data. Maybe it doesn't remove all the DDT entries, such as for metadata, but at least most of it will be gone. Turning off dedup only prevents deduplication of data you write after that act.

Daniel

On Oct 20, 2012, at 10:18 AM, David Wimsey <david at wimsey.us> wrote:

> I've had dedup on for a while and everything was good until the feeble machine I have as a file server couldn't deal with the memory requirements of dedup.  I solved the problem by adding more RAM, imported the pools on the machine and turned off dedup.  I had a ratio of less than 2x, and the main savings were on virtual machine disks which I want maximum performance for.
> 
> Does the memory consumption due to the DDT go away when you turn dedup off or do I need to do a send/recv on it?
> 
> I assume that once the block is deduced and written to disk its not really any different than a blocks associated with a snapshot, is that correct?
> 
> I also assume that there is no performance penalties on reads, only writes since it (with dedup on) has to check the dedup table to see if it is a duplicate, is that correct?
> 
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