Re: Odd behaviour of two identical ZFS servers mirroring via rsync

I thought I would report back that changed my rsync options from '-Wav 
--delete' to '-av --inplace --no-whole-file --delete' has made a 
significant difference, with mirrored directory sizes on the slave server 
now falling and approaching the original sizes on the master. The only 
downside is that since whole-file replication is obviously a lot faster 
than updating the changed parts of individual files, mirroring is now 
taking longer than 24 hours so this will be changed to every few days or 
even weekly when more is known about user behaviour on the master server.

Andy

On Sun, 13 Nov 2022, Bob Friesenhahn wrote:

> On Sun, 13 Nov 2022, Mark Saad wrote:
>>> 
>> Bob are you saying when the target is zfs --inplace --no-whole-file helps
>> or just in general when you have
>> large files ?  Also have you tried using --delete-during / --delete-after 
>> ?
>
> The '-inplace --no-whole-file' updates the file blocks if they have changed 
> (comparing the orgin blocks with the existing mirror blocks) rather than 
> creating a new copy of the file and moving it into place when it is complete. 
> ZFS does not check if data content has been changed while it is being written 
> so a write of the same data will result in a fresh allocation based on its 
> Copy On Write ("COW") design.  Writing a whole new file obviously 
> significantly increases the number of blocks which are written.  Requesting 
> that rsync only write to the file for the blocks which have changed reduces 
> the total number of blocks which get written.
>
> The above helps quite a lot when using snapshots since then fewer blocks are 
> in the snapshots.
>
> I have never tried --delete-during so I can't comment on that.
>
> Bob
> -- 
> Bob Friesenhahn
> bfriesen@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
> GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/
> Public Key,     http://www.simplesystems.org/users/bfriesen/public-key.txt
>
>


----------------------------
Andy Thomas,
Time Domain Systems

Tel: +44 (0)7866 556626
http://www.time-domain.co.uk