We manage our own facility - so having the backup server @ our facility works great.
In short here is the setup:
clients network ----
Gigabit Layer Switch
| |---->Backup Server-----> Storage Array
| SAN Array NAS Array
|----->routing / external network
We found by utilizing a NAS/SAN (we use both depending on what the servers are doing - ie block level access (SAN) for database servers etc... and NAS (file oriented) we were able to increase the efficiency of the network a ton.
For the simple backup - a NAS or SAN however will work.
When we tested this setup - it was pretty simple.
You can actually load the software on virtually anything - it will run on vanilla centos (and other flavors)
I have heard of people running it on the cPanel box - but seems kinda silly to do so if thats the box your backing up.
There is only 1 issue that I do not like about R1soft as of yet when it comes to cPanel.
The clients cannot restore their own databases...
The reasons for this are being worked out I hope... but in short they have to do w/ the location and way that cPanel stores the clients database files /var/lib/mysql (generally)
Having given our clients the ability to restore files from minutes ago - is awesome.
the cPanel integration is flawless - and our customers have been praising this backup system ever since we put it in place.
R1Soft is focused on clients as well... They care about the clients - their needs, desires, and understand your business requires a backup solution that works.
I did a quick hunt around - depending on your datacenter you may get buy with R1soft pretty cheap...
My suggestion however is go direct to Chris @ R1Soft - and purchase directly.
The software is only $500 for 5 servers and 1MySQL license (i can help you cluster mySQL if ever needed to get around needing more... and more licenses
If you were say - at the Planet - or GNax - or even in our DC - and you purchased your own cheapy server - you could buy the software outright - and then just ask for a vlan between the boxes -
this would save you a ton of cash in the long run - in under 2 months in fact you would have split even... !
For storage - if needed - you could also take a peek into
NetApps StoreVault S300 - its less than $3K for 1TB and has 4 10/100/1000 Ethernet ports - as well as being expandable up to 4TB
You could also build your own cheaper if you know how...
The Buffalo TeraStation Pro II is decent (slower i believe) but still decent.
Runs from $700 and allows up to 3TB Its simple SATA II - so an inexpensive method would be to buy the SATA drives (say those fancy 1TB drives from Seagate) and let the system go to town with them.
The system comes with USB / Ethernet and a few windows solutions in the box as well - (doubt you would need those yet for cPanel... but in the future. . . . )
Iomega has there StorageCenter Pro solutions however I have not tested these personally -
If your stuck let me know via PM and I will try to set some time aside to discuss your needs