ZFS storage and backup

[James]

On 15/11/2021 16:18, infoomatic wrote:
> Regarding
> storage I tend to use sdbox, from what I have read it seems to be the
> better option when using a COW filesystem compared to mdbox. One more

https://doc.dovecot.org/admin_manual/mailbox_formats/
sdbox   single-dbox, one message per file.
mdbox   multi-dbox, multiple messages per file.

so I guess sdbox is better with ZFS.  I could test each but I think I 
will find the IO used by dovecot is low for each.  I have one user with 
32,164 emails in INBOX and IO is not a problem.


> question is: compression at file system level or in dovecot storage?

System.  The OS compresses using all CPUs in a separate process. - does 
dovecot?  Dovecot is smaller and simpler (--with-zlib=no etc).  You can 
change the ZFS compression anytime.  Text files remain plain text files 
even though they are compressed on disc.

When available, zstd in ZFS should be a better option than gzip.


> The reason I am not sure to switch to ssds is that most servers are for
> non-profit organisations, sports clubs etc. - they also need some
> storage for pictures, their budget is quite low (so performance testing
> would only be done out of my interest), and if spinning rust with
> optimized settings suffices why not.

As you have the HDDs already wait until there is a problem before fixing 
it.  Over the internet I doubt anyone will notice and more importantly 
care enough to pay.  Your HDDs might be old and about to fail so other 
factors rise in importance.  Data security and continuity of service are 
more important than latency.

Do you have enough RAM for read cache?  A separate log for writes? L2ARC 
will only help if you have more active data than fits in RAM.


James