Hello,
I recently asked myself this question: Is it possible to unset ZFS
properties? Or reset one to its default state without looking up what
that default state is?
I believe the answer is yes, via the zfs inherit command (I haven't
verified yet, but I think a case could be made to add functionality to
the zfs set command...or the documentation...to make this clearer.)
An example:
You have a pool named tank.
You have created a filesystem called 'home' and it has a child
filesystem called 'smith'.
You run: zfs set compression=on tank/home
which turns on compression on the 'home' filesystem (it is a local
property) and on the 'smith' filesystem (as an inherited property).
(You inspect the properties with 'zfs get'.)
You then run: zfs set compression=on tank/home/smith
which makes compression on the 'smith' filesystem also be a local property.
At this point you decide you would rather that the compression property
for filesystem 'smith' be inherited after all, not be a local property
anymore.
You run:
zfs set compression=off tank/home/smith
but that doesn't unset the compression setting for filesystem 'smith',
it just overrides the inheritance of compression=on (as expected).
So how to unset/reset?
In looking for an answer I went back to the page where I found the
available properties and their valid parameters:
Introducing ZFS Properties
http://docs.sun.com/app/docs/doc/817-2271/gazss?l=en&a=view
I didn't see anything under 'zfs set' or under the 'compression' section
for how to unset a property. I did find a link to this page:
Setting ZFS Properties
http://docs.sun.com/app/docs/doc/817-2271/gazsp?l=en&a=view
which had a link to this page:
man pages section 1M: System Administration Commands
http://docs.sun.com/app/docs/doc/819-2240/zfs-1m?l=en&a=view
which talked about 'zfs inherit' and 'zfs set':
zfs inherit [-r] property filesystem|volume|snapshot ...
zfs set property=value filesystem|volume|snapshot ...
*****
In short, I think an alias for 'zfs inherit' could be added to 'zfs set'
to make it more clear to those of us still new to ZFS. Either that, or
add some additional pointers in the Properties documentation that the
set command can't unset/reset properties.
The alias could work like this:
If someone issues a command like this:
zfs set property=inherit filesystem|volume|snapshot
then run this code path:
zfs inherit property filesystem|volume|snapshot
The -r command could be added to 'zfs set' as well, to allow 'zfs set'
to recursively set local properties on child filesystems.
zfs set -r property=inherit filesystem|volume|snapshot
then run this code path:
zfs inherit -r property filesystem|volume|snapshot
Another example if zfs set was extended:
zfs set -r compression=on tank/home
would set a local property of compression=on for 'home' and each of its
child filesystems. (new functionality)
zfs set -r compression=inherit tank/home
would set the property of compression to default for 'home' and each of
its child filesystems. (alias of zfs inherit -r compression tank/home)
zfs set compression=inherit tank/home
would set the property of compression to default for 'home' and leave
the child filesystems properties untouched (alias of zfs inherit
compression tank/home)
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