Cyrus IMAP and MySQL mailboxes (Building load-balancing cluster)

[Sarah Walters]

> -----Original Message-----
> From: Simon Matter [mailto:simon.matter at invoca.ch] 
> Hi Sarah,
> 
> I'm really confused now.
> 
> 1) You are talking about NAS as a possible solution and I 
> don't know how
> that should work if NFS doesn't work. Until now I thought a 
> NAS device is
> an embedded fileserver which can be accessed using different network
> filesystems like SMB/CIFS, NFS or whatever. As long as it 
> doesn't provide
> proper locking (which may only be true if it provides NFSv4), it will
> never work as a shared storage among more than one cyrus-imapd server.

As I said in an earlier post, NFSv4 only. And I haven't tested this, I
am just saying that v4 is *supposed* to sort out the locking issues. I
used to work in an NAS environment, am in a SAN environment now (though
Cyrus is on local disk for budgetary reasons I won't go into here). All
of the above is correct.
 
> 2) Several people on this list have confirmed that they are running
> cyrus-imapd clusters on shared storage (SAN) which works fine with a
> cluster filesystem. That tells me that shared access to cyrus 
> databases
> works fine as long as the filesystem used provides proper 
> locking, which
> means in case of a cluster that the cluster filesystem has to 
> coordinate
> locking among all cluster members. Isn't that the main reason 
> why those
> filesystems exist?

If it works, great. I haven't worked with this kind of cluster before,
so I don't have any experience with it. What I said is that *database*
locking is in the OS, not the filesystem, and as such the clustering
software wouldn't actually work. As another post (by Janne) pointed
out, if you avoid BDB then this isn't an issue because you would be
using filesystem locking.
 
> 3) I don't think the reliability of an appliance hardware is 
> any better
> than good server and SAN components. In fact most appliances I saw are
> simply relabeled DELL or Intel OEM hardware. What you say may 
> be true for
> the installed software but I don't think it's true for the hardware.

I have used an excellent appliance in a prior workplace, but as I
haven't been there for a couple of years now I don't have recent data
and as such won't comment on the brand. But as it is known hardware,
you can have a much leaner operating system with all components
properly tested in a professional laboratory to ensure that they
work well together. Every patch is tested for impact on the entire
system. The appliance I had in mind is still Cyrus at its guts I
believe. It was merely another option to consider. The nice thing
about appliances is that management types can't hijack the spare
CPU cycles for their "project of the week" :)

Regards,
Sarah Walters