> From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss-
> boun...@opensolaris.org] On Behalf Of Koopmann, Jan-Peter
> all I can tell you is that I've had terrible scrub rates when I used dedup. 

I can tell you I've had terrible everything rates when I used dedup.

> The
> DDT was a bit too big to fit in my memory (I assume according to some very
> basic debugging). 

This is more or less irrelevant, becuase the system doesn't load it into memory 
anyway.  It will cache a copy in ARC just like everything else in the pool.  It 
gets evicted just as quickly as everything else.

> Only two of my datasets were deduped. On scrubs and
> resilvers I noticed that sometimes I had terrible rates with < 10MB/sec. Then
> later it rose up to < 70MB/sec. After upgrading some discs (same speeds
> observed) I got rid of the deduped datasets (zfs send/receive them) and
> guess what: All of the sudden scrub goes to 350MB/sec steady and only take
> a fraction of the time.

Are you talking about scrub rates for the complete scrub?  Because if you sit 
there and watch it, from minute to minute, it's normal for it to bounce really 
low for a long time, and then really high for a long time, etc.  The only 
measurement that has any real meaning is time to completion.

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