The best method we've found is to install DB/Web/Dialer in your most powerful server (whatever that is). This is not related to hard drive space, but core count, CPU speed and Memory. Memory can be added later if you need it to pump up your system when you get time to do so.
Next up you'll need one or two Web servers (two is best for redundancy). These servers do not need to have any Vicidial processes/screens running on them. They are only for web. (We usually install everything and then just turn off the cron jobs ... so these servers can become dialers in a pinch!) Web servers can have tiny HDs. Seriously. We've got some with 20G.
Then you add all the rest of your servers as dialers. We also include web services in these servers to allow (once again) them to be used for web servers in a pinch and to allow access to recordings before they get pushed to the archive server. This way you can leave your recordings on the dialers longer if you choose to do so in addition to being able to use the dialers for web services if you need it. Dialers can have tiny HDs as well, but beware the recordings. If you put in 146G SAS or SSDs, then you can likely hold an entire day's worth of recordings if you want to ...
Any of the servers can be the Archive server if you add a huge HD. This server will be difficult to use for anything else unless you collect all your recordings onthe dialers during the day and push to the archive after shift. Most centers have a dedicated but 'underpowered' server for the archive server. It needs a big HD, but it does not need a lot of cores or fast cores or even a lot of memory.
Be careful with the archive server's HD. After recordings are pushed there, those are the only copies of the recordings. Having an external FTP service (off-site, another office for instance) to make a full copy of the archive server's HD is a great idea. You can use rsync or the "built in to Vicidial" ftp2 scripts for full automation.
You'll need to be very aware of your internal network and firewalls. Vicidial to carrier firewall especially. If your IT staff has experience with HIGH call volume networking it can still be a headache. But if they say that their "non-high-call-volume" experience will get them through, you should leave an extra week of "ramp up" time for the inevitable networking issues that Vicidial will throw at your systems. The Vicidial Group (and we at PoundTeam) are used to those perplexed phone calls where a call center reaches 150 agents and suddenly the "great planning" network falls apart. Avoid pfSense when using Vicidial (use it, but don't pass the Vicidial calls through it!). If possible, let the IPTables firewall already in Vicibox become a whitelist-based firewall and limit communications to the Carrier Only. Vicidial should share an internal IP/network with agents and the Cluster ... and each server should have its own public IP protected by the whitelist. Then you do not need a second firewall and there's one less link in the chain to fail. We published Dynamic Good Guys (Free on ViciWiki.com) a few years ago, which includes instructions for pure whitelist before installation. Continuing after the whitelist to install DGG is merely to give you a simple web-based interface to add whitelisted IPs and can also be used to allow the boss to hit the Real time screen from Starbucks (and external agents whose IPs change daily to get in without any fuss, while remaining secure!).
And don't let Matt get you down about Dell. We use nothing but Dell here, LOL.
(We've only had three SuperMicro servers in 10 years ... all three have died and been scrapped!)