I want to build an external drive that will last 5 to 6 years. This was prompted by needing more space on my LaCie 1TB external drive. I am looking to build a external drive with components that are better than the ready made kind so I can swap out parts as technology changes (e.g. larger capacity drives, faster connections, more efficient power supplies) and if individual parts fail. My Mac Pro is running 10.5 and will upgrade to 10.6 shortly after it arrives. I use Time Machine to do the back ups to my external drive. Any recommendations are greatly appreciated.
I am looking to build a external drive with components that are better than the ready made kind so I can swap out parts as technology changes (e.g. larger capacity drives, faster connections, more efficient power supplies) and if individual parts fail.
So basically, you want to build a NAS (Network Attached Storage) out of computer parts to get flexibility & upgradability, is that it?
If so, probably any cheap PC, even 5-6 years old, is probably "better" than the "ready made" ones. Since they will be dedicated for storage, you can probably use software RAID if the PC you will be using doesn't have it built-in. For OS, I would use FreeNAS.
However, one thing I feel I have to mention is that a DIY NAS out of old parts might consume significantly more electricity than the "ready made".
I don't think OP was going as far a NAS. Just an external hard drive, but with upgradable hardware (for capacity, etc) and lifetime >5 years preferred. For this, buying separately an external enclosure and a high-reliability hard drive seems best. I'm not familiar with Mac Pro's, so I don't know what ports are available to connect from the Mac to your external. Probably USB2, maybe eSATA or Firewire 400 (aka IEEE 1394a). On some Macs you might even find Firewire 800 (aka IEEE 1394b). Of these, Firewire 800 is fastest, Firewire 400 and eSATA are very fast, and USB2 is slower but VERY widely used on almost every machine. Get an enclosure with two or three possible interfaces to cover current and future needs. Make sure the internal connectors in the case are for the type of HDD you buy - this is separate from the connection system between case and computer. I would definitely choose SATAII hard drives to put in the case.
Sometimes people have had difficulty mounting very large HDD's over 1TB in certain external cases, so check manufacturer's specs on that. Some external cases will accept 2 HDD's, not just 1, so you can build a monster external that way.
For longevity of the drive(s) installed, MAYBE you want an enclosure with fan cooling. That depends on how hot the drives normally run, and on the anticipated load cycle - will they be used a lot, or on occasion? My main concern with fan cooling is the longevity of the fan itself - I'd be really tempted to buy now one or two replacement fans for the enclosure, in case you can't find one 4 years from now.
From the power consumption perspective, an external likely will be similar to a small NAS unit, but both will consume less than an old general-purpose computer reconfigured. On the other hand, of course an NAS unit is available to all computers on your network, not just to the one computer an external unit is attached. But I think OP was not worried about network access to this resource.