zfs primarycache and secondarycache properties [PSARC/2008/393 FastTrack timeout 06/27/2008]

[Darren J Moffat]

Jeff Bonwick wrote:
> The L2ARC seems more complex because allocation is done by the feed thread,
> not in the context of any particular dataset doing I/O.  The feed thread
> has no way of knowing on whose behalf blocks exist.  So it would have to
> operate as it does today, caching everything that falls out of the ARC.
> It's not clear to me how the L2ARC policy can be anything other than a
> pool-wide property.

I had to solve a very similar problem for enabling encryption support in 
the L2ARC.  I did this by using the internal flags field in the ARC 
header to record wither or not the the initial read/write in the ARC was 
for an encrypted dataset.  I think this case is slightly tricker but I 
can see how it could be done.

-- 
Darren J Moffat