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Re: cgd + zfs

Greg Troxel <> writes:

> Brad Spencer <> writes:
>>> I'm now thinking, would it make sense to do the layering the other
>>> way around, i.e. have cgd on top of a zvol?  I wonder if there would
>>> be any resilience (and possibly performance) advantage to having zfs
>>> directly access the hard drives (which, being old and bought off
>>> ebay, I don't quite trust) rather than go through cgd.
>> To be honest about it, I don't remember if I tested in that direction.
>> It would be simple enough to try.  You just might have the same problem
>> with missing IOCTLs that keeps swapping from working.
> If you put cgd on zvol, then what filesystem are you putting in the cgd?
> Another zfs pool? ufs2?   To me, zfs on cgd makes more sense, because
> then you actually get zfs, and can have raidz2 or whatever, but all
> media is encrypted.

I was speaking only of the attempt to do this, not the reason why
someone might want to do this.  As to what you may want to use.. I
honestly would hope that anything would be possible with stackable
filesystems....  As you suggest the question of why and what??  Well...
one I can think of is to make a portable, but fully encrypted, container
that would allow for 'zfs export' to be a trival thing or at the very
least allow you to write out just a part of a pool or drive and be
assured that it is encrypted and contained.  I do something like this a
bit between MacOS, NetBSD and sometimes FreeBSD, of course without
encryption (I do understand that cgd isn't avaliable everywhere).  Of
course, you could also put a FFS on it.  I have tested FFS on a zvol and
it works, but I didn't try cgd, but it isn't hard to imagine layering in
encryption too.  But I do agree with you that zfs on cgd probably makes
the most sense in the common case if you don't have to move anything
around too much or slice out a contained portion of the storage.

Brad Spencer - - KC8VKS -

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