NFS vs Replication

[Coy Hile]

> On Jul 15, 2020, at 12:33 PM, Andrea Gabellini <andrea.gabellini at telecomitalia.sm> wrote:
> 
> Hello list,
> 
> I built an email system using a proxy / director pair (IMAP, POP3, LMTP)
> and a backend pair.
> 
> To have an HA system, I would like to understand if it is better to use
> an NFS export or replication to save emails and index files
> 
> NFS is provided by a NAS (in HA), while for replication I would use the
> local backend disks
> 
> Which of the two systems is more reliable? Are there any drawbacks for
> one or the other?
> 

The biggest problem with using NFS is that you’re using NFS and bringing
along all the baggage that comes with it. Writes over the network are
inherently slower than writes to local storage, plus locking gets interesting,
to say the least.

I posted a while back about using something similar to Joyent's manatee to
bootstrap replication. (If IMAP replication works anything like databases,
a system could join the cluster, get a base state by streaming a ZFS snapshot
of an existing peer to the new peer, and from there it catches up via the normal
replication mechanisms.) I don’t know if that would be feasible, but it’s certainly
something I might try to make work. I also don’t know whether it gets more dicey in
a multiple-primary situation.)

But long and short of it. Avoid NFS if you can. The last time I used NFS for mail was
last century, and even with everybody using native *nix MUAs like pine and elm, we
could run into fun locking issues.

--
Coy Hile
coy.hile at coyhile.com