Read-only view of a ZFS filesystem inside a bhyve guest?

Daniel Braniss danny at cs.huji.ac.il
Sat Apr 28 11:28:24 UTC 2018



> On 28 Apr 2018, at 14:26, Daniel Braniss <danny at cs.huji.ac.il> wrote:
> 
> 
> 
>> On 28 Apr 2018, at 13:37, Mark Raynsford <list+org.freebsd.virtualization at io7m.com> wrote:
>> 
>> On 2018-04-28T09:08:42 +0300
>> Daniel Braniss <danny at cs.huji.ac.il> wrote:
>> 
>>> since the clients and the server are sharing the zfs volume,
>>> I’m doing the following:
>>> on the server I did:
>>> 	zfs create -sV 4G h/root.ro <http://root.ro/>
>>> 	newfs /dev/zvol/h/root.ro <http://root.ro/>
>>> 	mount /dev/zol/h/root.ro <http://root.ro/> /mnt
>>> 	copy a working root image to it.
>>>       umount /mnt
>>> 	the clients then mount it as ro,
>>> 	the vm conflg file has:
>>> 		disk0_type=virtio-blk”
>>> 		disk0_name=“/dev/zvol/h/root.ro <http://root.ro/>”
>>> 		disk0_dev=“custom”
>>> 
>>> one solution to the fact that the root is read-only is to use unionfs (probably nullfs will do too)
>>> 
>>> the only problem I have is updating the image.
>> 
>> Wow, didn't know this was possible. Is this safe? Two essentially
>> independent operating system instances being able to write to the same
>> zvol?
> 
> that’s why it’s mounted rear-only in the client!
grr, hate spell checkers, s/rear/read/ :-)

> each client can get another vol for writing, ie /var
> if you want to have ‘permanent’ changes that will survive reboots.
> 
> updating on the server is possible, but
> 	1- the changes might not be seen by the client
> 	2- opened files will have issues
> 
> btw, point 2 is also true for NFS.
> 
> danny
> 
>> 
>> -- 
>> Mark Raynsford | http://www.io7m.com
>> 
> 



More information about the freebsd-virtualization mailing list