I see your previous post - quite an impressive setup. I didn't know that the mini's could take in two drives (so you have raid-0/1 on the mini?). I guess for me the biggest issue would be to have individual drives with no redundancy attached to the mini (all USB or FW?) unless OS X server is somehow able to stripe across them (don't know how this would work). Do you then have all the external drives and the mini UPS'ed and if so, how do you avoid any storage issues, since a UPS would eventually run out of juice and pull power (I guess the OS X server would unmount file-systems properly and do a proper shutdown).
I treat the Synology as a server-/storage-tier - so the Synology does the Timemachine backups, Squid, DHCP, DNS, network shares, iTunes libraries as well as web applications for cloud services (photos/video I share with relatives via the web). I then run gigabit across the house (for media playback) and a number of wifi hotspots.
I guess the mini will scale out to a certain level but will never have true redundancy. With the current Synology I run 15TB of raided storage and go transparently (without major rebuild) to expansion modules or rackmount if I choose. I think it really just depends on the OP's budget and short/mid term plan.
Yes they can, 2nd drive was always in place of the DVD.
For a new technically oriented buyer I'd always suggest buying a single low capacity drive, and do the upgrade yourself; quite easy and way cheaper, the same goes for OSX Server, rather buy this from the Mac App store.
I essentially have:
Older mac mini has a FW & USB connected multi drive storage units, newer mini has Thunderbolt and USB 3 storage units. To ensure I loose nothing, I have shell scripts that ensure content backups; these scripts are triggered by changes in a folder; for example: change or add a file triggers a copy to the backup location.
However if you prefer your version of 'true redundancy', then nothing prevents you from connecting the mini to an external Thunderbolt raid controller with fibre channel which the affords it to be wired into a fibre channel SAN of any size. Apple also has a tried and tested XSAN solution (which btw comes with OSX server).
http://en.wikipedia.org/wiki/Xsan.
Btw I don't agree, the mac minis don't scale out so easily, especially the new ones with Thunderbolt, and Google has many examples of how the minis are used in a rack environment with large SANs
The point I'm trying to make is that the mini affords you a lot of flexibility; it is essentially another mac computer and therefore won't be limited to only an initial set of features (that where I feel the synology fails in comparison); remember any Mac (computer) can be easily enhanced beyond basic use through the addition of software, hardware, custom scripting, ...