On Dec 6, 2012, at 5:30 AM, Matt Van Mater <matt.vanma...@gmail.com> wrote:

> I'm unclear on the best way to warm data... do you mean to simply `dd 
> if=/volumes/myvol/data of=/dev/null`?  I have always been under the 
> impression that ARC/L2ARC has rate limiting how much data can be added to the 
> cache per interval (i can't remember the interval).  Is this not the case?  
> If there is some rate limiting in place, dd-ing the data like my example 
> above would not necessarily cache all of the data... it might take several 
> iterations to populate the cache, correct?  
> Quick update... I found at least one reference to the rate limiting I was 
> referring to.  It was Richard from ~2.5 years ago :)
> http://marc.info/?l=zfs-discuss&m=127060523611023&w=2
> I assume the source code reference is still valid, in which case a population 
> of 8MB per 1 second into L2ARC is extremely slow in my books and very 
> conservative... It would take a very long time to warm the hundreds of gigs 
> of VMs we have into cache.  Perhaps the L2ARC_WRITE_BOOST tunable might be a 
> good place to aggressively warm a cache, but my preference is to not touch 
> the tunables if I have a choice.  I'd rather the system default be updated to 
> reflect modern hardware, that way everyone benefits and I'm not running some 
> custom build.

Yep, the default L2ARC fill rate is quite low for modern systems. It is not 
to see it increased significantly, with the corresponding improvements in hit 
rate for
busy systems. Can you file an RFE at 
 -- richard



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