Backup Server Configuration Questions

Question

I have a super little setup for our small business consisting of 1 primary mac mini server, 1 backup mini server, 2 WD 2TB external firewire drives, and a rackmounted Cisco switch and UPS. AFP, VPN, FTP, expandable storage, time machine backups and managed mobile accounts all packed into a compact, quiet server cabinet that fits under a desk for less than $2000. Unfortunately the success of this little gem has made it more and more critical to our publishing workflow.
For good measure I picked up another mac mini thinking i could set it up as an OD replica backup server. Unfortunately I didn't think this through before the purchase and now I have a what amounts to $500 brick in my server cabinet. Would appreciate some guidance on how best to deploy this backup server.
1) For the backup server to be of any real use I assume its going to need access to the data drives. Is there any way to manage this with external drives? Somebody suggested I should just plug my external drives into both servers, however I did some other reading that suggested this could turn my drives into toasters. I then thought of setting up WD NAS drives through my cabinet switch but was told that NAS and AFP don't play well and I would have the same issue - two systems trying to access the filesystems at the same time.
2) If i can resolve the first issue, I have the backup setup as an OD replica, which theoretically should take over if the primary goes down. Do I also need to setup DHCP on the backup for this to be relevant? Should that range be the same as the primary or do they need to be distinct?
3) I have the 2TB primary drive firewired to the primary server with the 2TB time machine drive daisy chained. I was recommended to use Syncronize Pro for my backup between the drives but despite the warnings on time machine's applicability in a server setup (timing not configurable, CPU overhead) its been perfect for my needs with zero CPU overhead after the first sync. My only complaint is time machine doesn't work with ARD so you have to browse the time machine directory manually.
4) Am I missing a larger plot here? Can I setup the external drives or backup server in another way to be more efficient. Should I pickup another set of drives and somehow synchronize the primary and secondary server completely??
This is my first server config and has been a fun little project except for a nightmare of a time with the VPN but that's another story.
Any help apprecaited.

Answer 1

For the backup server to be of any real use I assume its going to need access to the data drives. Is there any way to manage this with external drives? Somebody suggested I should just plug my external drives into both servers, however I did some other reading that suggested this could turn my drives into toasters.
You're right - You cannot connect one FireWire drive to two systems and hope it will work. That is asking for trouble right there.
I then thought of setting up WD NAS drives through my cabinet switch but was told that NAS and AFP don't play well and I would have the same issue - two systems trying to access the filesystems at the same time.
The whole point of NAS is that the NAS controller (in conjunction with the access protocol (e.g. AFP, NFS, etc.) takes care of concurrent access.
However, all of the above depends on the data you're storing on the external/shared drives. For example, don't expect to store any database-based data such as Open Directory to be shared between machines via the shared drives. Any shared drive setup should be for static files only (e.g. users home directories would be OK, as would backups, web content, etc.).
I have the backup setup as an OD replica, which theoretically should take over if the primary goes down. Do I also need to setup DHCP on the backup for this to be relevant? Should that range be the same as the primary or do they need to be distinct?
That depends on what you're trying to protect against.
If you're planning to keep critical services running in case the primary server fails then you can probably eschew DHCP altogether - existing clients will retain their DHCP address for at least half the lease period. e.g. if your lease is set for 3 days you have 36 hours before those machines will require a functional DHCP server. That's more than enough time for most server issues to get resolved (e.g. a reboot), and even more than it takes to turn on DHCP on the secondary server if you don't think the primary server will be back online in time.
IMHO that's preferable to running dual DHCP servers. You can do that if you prefer but they MUST have different DHCP ranges (don't try to setup both DHCP servers with the same address pools).
As for point 3 - Time Machine is fine, IMHO, as long as you realize its limitations and don't expect Time Machine to backup everything, including dynamic data such as database files.
4) Am I missing a larger plot here? Can I setup the external drives or backup server in another way to be more efficient. Should I pickup another set of drives and somehow synchronize the primary and secondary server completely??
It depends on what you're preparing for/against.
If you're looking to protect against hardware failure then you could run everything on the external drives and reconnect the drives to the other machine to boot it as the server if the first one is down. That's not necessarily ideal, but it would be one option.
The second thing to consider is what services you're running that support their own replication/backup protocols. You've already seen Open Directory replicas, so that's the right way to backup your OD setup. The same applies to DNS and MySQL - both of which have their own replication protocols.
User-based data is a little harder to replicate between servers which is why a NAS option may be viable here. Of course that doesn't necessarily provide protection against accidental deletion.
At the end of the day, though, there are many ways to set this up. The right way depends on your needs, the services you're running and what's important to your business (focus on the things your business cannot do without, and have a plan for the other services (e.g. manually start the secondary DHCP server if needed.