Could I ask how large your Zentyal install is, and what services are installed to use that much space? A rough list would be fine, I don't want you having to dig out huge lists of what your server does: it's just so I can have an idea of what services it provides.
Does size matter ?
Sorry, joking
I mean, more than size (this is still "SMB like" for about 4 to 6 users) what really matters is how you configure services.
From HP server standpoint, notice I'm running customized BIOS allowing HDD hot-plug and AHCI (SSD without AHCI is waste of money)
My Zentyal platform is acting as internet gateway, meaning FW, HTTP proxy, mail (+ additional mailing list server), VPN (I've few remote users), OwnCloud.
Obviously users & groups.
File sharing is deployed and configured but I'm only using WINS features as my NAS is another HP N40L running OpenMediaVault (relying on Zentyal LDAP).
Few web sites (vhost) to support, e.g. WPAD, webmail, OwnCloud (notice my mail service is standard mail. I don't need Zarafa)
DNS, DHCP, anti-virus and mail filtering are pretty obvious I suppose
As I don't need all the 3.0 bells and whistles, I'm also still running 2.2
Last (and least
) this platform implements multiple NICs in order to benefit from failover (multiple ISP) and also provide DMZ hosting another Zentyal (3.1 sandbox). On the other hand, I do not run any local X interface like gnome, unity or LXDE. That's a server isn't it? No keyboard nor display
What will really impact such platform is the heaviness and complexity of HTTP proxy.
Loading specific and complex filtering rules will have direct impact on performances.
Heavy usage of CIFS may also impact your platform (tested from OpenMediaVault
)
I hope this helps.
If I had to comment further your choice, allocating 250GB HDD as Zentyal system disk is waste of resource. 32GB is more than enough.
Power supply is not that big, neither air cooling. If you run 4 disks + powerful video card, pay attention to this.