zfs discuss - Dec 2010 - ZFS send/receive while write is enabled on receive side?

Hi all, from much of the documentation I''ve seen, the advice is to set
readonly=on on volumes on the receiving side during send/receive
operations. Is this still a requirement?

I''ve been trying the send/receive while NOT setting the receiver to
readonly and haven''t seen any problems even though we''re
traversing
and ls''ing the dirs within the receiving volume during the send/recv.

So, is it OK to send/recv while having the receive volume write enabled?

-Moazam

On 12/10/10 12:31 PM, Moazam Raja wrote:
> Hi all, from much of the documentation I''ve seen, the advice is to
set
> readonly=on on volumes on the receiving side during send/receive
> operations. Is this still a requirement?
>
> I''ve been trying the send/receive while NOT setting the receiver
to
> readonly and haven''t seen any problems even though we''re
traversing
> and ls''ing the dirs within the receiving volume during the
send/recv.
>
> So, is it OK to send/recv while having the receive volume write enabled?
>
That depends how you define OK!

A ZFS receive will fail (cleanly) if you don''t use -F and if you change
data on the receive side.

A write can fail if a filesystem is unmounted for update.

-- 
Ian.

On Thu, Dec 9, 2010 at 5:31 PM, Ian Collins <ian at ianshome.com>
wrote:
> ?On 12/10/10 12:31 PM, Moazam Raja wrote:
>> So, is it OK to send/recv while having the receive volume write
enabled?
> A write can fail if a filesystem is unmounted for update.
True, but ZFS recv will not normally unmount a filesystem.  It could
if you are receiving an incremental "send -R" stream where the
mountpoint or canmount properties are changed.

If you are accessing a file that is deleted by "zfs recv", then you
will get ESTALE.

--matt

On Dec 9, 2010, at 3:31 PM, Moazam Raja wrote:
> Hi all, from much of the documentation I''ve seen, the advice is to
set
> readonly=on on volumes on the receiving side during send/receive
> operations. Is this still a requirement?
> 
> I''ve been trying the send/receive while NOT setting the receiver
to
> readonly and haven''t seen any problems even though we''re
traversing
> and ls''ing the dirs within the receiving volume during the
send/recv.
> 
> So, is it OK to send/recv while having the receive volume write enabled?
As others have mentioned, the changes can be automatically removed
during the next receive.  If that is ok, then it is ok.

For NexentaStor''s auto-sync service, by default, we do not mount the
receiving file systems. We do offer an option to automatically clone
the receiving file system snapshot, so you can have a writable copy
that doesn''t get destroyed by a future receive.
 -- richard