So, just to recap - you're wondering how long it will take to transfer a (roughly) DVD-sized file from your fathers server? And obviously you don't want to interrupt his bittorrents too much while doing that? Hmmm, what business did you say he was in again?
A couple errors need to be cleared up in this RAID5 love-fest however:
Regardless of how many drives you have in a RAID5 array, only the storage from (1) of the drives is dedicated for redundancy, yet ANY one drive in the array can fail and you can still get all your data.
Not true, no drive is dedicated for redundancy in RAID5. Redundancy is spread across all drives in a RAID5 array. Newbie error
For RAID-5, you need a minimum of (3) drives. One of the nice things is that if you buy a RAID-5 controller with 6 or 8 or 12 ports and just start with your 4 drives in it, you can upgrade the storage on the fly. So for instance you start by connecting your (4) 250GB drives in RAID5 on a controller that supports up to (8) drives. This gives you 750GB of storage to start with, and if you decide in 6 months that you need more storage, just add a 5th 250GB drive and you'll have a full 1TB of usable storage!
Not bloody likely. Unless you have been VERY careful and have managed to find a PC card that will support RAID5
re-layout on-the-fly (and most definitely DO NOT), then this will not work at all without your backing everything up, tearing down the array and recreating it, and restoring it. You sound to the layman like you know all about this stuff, but I'm afraid this is a very basic assumption that just doesn't work in the sample adapters you have provided. Nor did you point that out either. Shame on you, misleading the OP!
Further, if you have 5 drives installed in a RAID5 and online relayout and backup/recreate/restore is not an option, then ALL you can do at this point is add another complete seperate 3 drive RAID5 volume (or 2-drive R1 mirror). Which won't be part of the original volume. Consider the physical limitations of what you can add as well - if you fill 6 slots of your 8 and want to continue with another raid5, well your minimum to add is another 3 disks, and where are they going to go?
Keep in mind, though, that with any RAID solution, the entire array will perform according to the slowest / lowest storage device in it.
Well, not really either. Though your following statement
For instance, if you have (5) 250GB drives and (1) 100GB drive in a RAID5 array, it's no better than just having (6) 100GB drives -- you'll only have 500GB of usable storage.
suggests you really meant capacity rather than perfomance so perhaps this was just a simple mistake...
Incidentally, I'd quibble the point that for a simple file server (nothing more) that hardware raid is an
absolute must - it's perfectly reasonable to use software raid5 given that the cpu will be idling its life away most of the time. Might as well give it something to do. Though my preference is for hardware raid given that you can use it for your boot volume as well of course. Downside - card dies, you need to find the same model to replace it or all your data is lost.