some ZFS questions

Daniel Staal DStaal at
Fri Aug 8 16:08:20 UTC 2014

--As of August 8, 2014 2:06:05 AM -0500, Scott Bennett is alleged to have 

>> > If I have one raidzN comprising .eli partitions and another raidzN
>> > comprising a set of unencrypted partitions on those same drives, will
>> > I be able to export both raidzN pools from a 9-STABLE system and then
>> > import them into, say, a 10-STABLE system on a different Intel amd64
>> > machine?  By your answer to question 1), it would seem that I need to
>> > have two raidzN pools, although there might be a number of benefits to
>> > having both encrypted and unencrypted file systems allocated inside a
>> > single pool were that an option.
>> Having any physical disk be a part of more than one pool is not
>> recommended (except perhaps for cache and log devices where failure is
>> not a big deal). Not only can it cause thrashing as you mentioned above,
>> but one disk dying makes both pools degraded. Lose two disks, and you
>> lose both pools. If you need only
>      If ZFS has no way to prevent thrashing in that situation, then that
> is a serious design deficiency in ZFS.

ZFS groups IO into batches to try to help against thrashing (and to improve 
efficiency), which could help.  But I'm not sure how it's supposed to work 
out when you give it two different devices that those are actually one 

While the normal 'preferred' setup for encrypting ZFS pools is to make the 
pool out of encrypted partitions, from your questions I'd argue that 
looking for ways to build the encryption on top of the zpool is probably 
the better route for you.  (I think you should be able to do that with 
geli, though I can't say I've ever played with it.)

Daniel T. Staal

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