On Jan 7, 2012, at 8:59 AM, Jim Klimov wrote:

> I wonder if it is possible (currently or in the future as an RFE)
> to tell ZFS to automatically read-ahead some files and cache them
> in RAM and/or L2ARC?

See discussions on the ZFS intelligent prefetch algorithm. I think Ben 
description is the best general description:

And a more engineer-focused description is at:
 -- richard

> One use-case would be for Home-NAS setups where multimedia (video
> files or catalogs of images/music) are viewed form a ZFS box. For
> example, if a user wants to watch a film, or listen to a playlist
> of MP3's, or push photos to a wall display (photo frame, etc.),
> the storage box "should" read-ahead all required data from HDDs
> and save it in ARC/L2ARC. Then the HDDs can spin down for hours
> while the pre-fetched gigabytes of data are used by consumers
> from the cache. End-users get peace, quiet and less electricity
> used while they enjoy their multimedia entertainment ;)
> Is it possible? If not, how hard would it be to implement?
> In terms of scripting, would it suffice to detect reads (i.e.
> with DTrace) and read the files to /dev/null to get them cached
> along with all required metadata (so that mechanical HDDs are
> not required for reads afterwards)?
> Thanks,
> //Jim Klimov
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