Some ZFS questions

David Christensen dpchrist at
Tue Apr 18 04:05:03 UTC 2017

On 04/17/2017 11:41 AM, Andrea Venturoli wrote:
> Hello.
> I'm a novice to ZFS and right now I'm conducting some experiments on
> 10.3. I've got some questions which might be obvious or FAQs, but I can
> assure I looked for an afternoon and found no answer.

> I first installed from the USB image and choose Auto-ZFS options when
> the installer came to partitioning.
> The install was succesful and "zfs list" would show something like the
> following (please note this is not an exact copy & paste, since I
> destroyed that install in the meantime):
>> zroot                781M  93.2G   144K  none
>> zroot/ROOT           777M  93.2G   144K  none
>> zroot/ROOT/default   777M  93.2G   777M  /
>> zroot/tmp            176K  93.2G   176K  /tmp
>> zroot/usr            616K  93.2G   144K  /usr
>> zroot/usr/home       184K  93.2G   184K  /usr/home
>> zroot/usr/ports      144K  93.2G   144K  /usr/ports
>> zroot/usr/src        144K  93.2G   144K  /usr/src
>> zroot/var           1.20M  93.2G   608K  /var
>> zroot/var/crash      148K  93.2G   148K  /var/crash
>> zroot/var/log        178K  93.2G   178K  /var/log
>> zroot/var/mail       144K  93.2G   144K  /var/mail
>> zroot/var/tmp        152K  93.2G   152K  /var/tmp
> What puzzles me is "zroot/ROOT": why do we need that? Why do we mount
> "zroot/ROOT/default" as root instead of simply mounting "zroot" at /?

Many data set properties are inheritable.  So, you could set some 
properties on zroot that affect the entire pool, set some properties on 
zroot/ROOT that affect all root file systems, and set some properties on 
zroot/ROOT/default for your default root environment.

I haven't tried it, but AFAIK it is possible to have multiple root data 
sets (e.g. "file systems").  So, if/when you create another root 
environment, say zroot/ROOT/custom, it will inherit such properties from 
zroot and zroot/ROOT.

I'm still a ZFS noob, so I'll pass on your other questions.


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