@Tater,
I understand your desire to re-cycle your old computer. It's that FreeNAS is an appliance
like software with specific hardware desires and requirements. Part of our harshness for the
hardware requirements, is that people have ignored them, or did not care when they put
their FreeNAS together. Then, when something bad happens, or even something annoying,
(like low performance), the person comes here to solve it. When in reality the solution is to
do the correct thing and
use proper hardware.
We care about reliability and recoverability of our data, thus, we use and recommend server
hardware. Some of us are computer professionals, and server room planning is in our blood.
Thus, I prefer to plan for 3 to 5 years without any changes, (space or performance upgrades).
All that said, you can use your old PC for backups. Test FreeNAS out on the hardware. Play
with it. I highly recommend that if you have a person using this FreeNAS for a dumping
ground, it's not their only place the data is stored.
Next, you will NEED 8GBs of RAM. If you can't get DDR2 memory today, then scrap the
idea of using FreeNAS. Few people run FreeNAS with less than 8GBs of memory. Some
who do, end up with problems.
A simple 2 disk Mirrored vDev ZFS Pool is perfectly fine. The performance is probably
just fine using 1Gbps or less Ethernet. The speed limiting factor might be the CPU or the
DDR2 memory, (don't know if that CPU uses FSB, Front Side Bus).
If you don't have more than 2 SATA ports, then you will have to use a USB drive for the
boot device. (Or 2 mirrored, since USB flash drives are not as reliable as they can be.)
Note that in the past, FreeNAS needed only 8GB boot devices. But, today, we recommend
16GB or a bit larger.
Last, read up on ZFS. It has some limitations, but in general it's a world & enterprise class
file system and volume manager. Not only does ZFS want to store your data, it wants to
protect it from harm.