zfs discuss - Feb 2010 - lofi crypto pools and *cache properties

Until zfs-crypto arrives, I am using a pool for sensitive data inside
several files encrypted via lofi crypto.  The data is also valuable,
of course, so the pool is mirrored, with one file on each of several
pools (laptop rpool, and a couple of usb devices, not always
connected).

These backing files are each in thier own dataset, on their respective
pools.  I have dedup and compress on within the pool, and off for the
backing datasets.

The ARC will contain data from the inner pool, of course, and this is
plaintext.  I don''t have an l2arc in the laptop, but if I did, I would
set secondarycache=none for all datasets in the encrypted pool to
prevent cleartext data being written to it.

However, should I set anything on the datasets holding the lofi
backing files?   The concern here is the possibility of double- (or
even quadruple-) caching, once for the plaintext data, and once each
for the mirrored lofi encrypted files. 

I have set primarycache=metadata for each of the /pool/lofi datasets
holding these files, just in case.  Is this necessary, or does lofi
already take care of this issue (via directio, or whatever)?

--
Dan.
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