I have a very large collection of blurays and DVDs that I am in the process of backing up to hard drives via MakeMKV. I was looking into building a NAS but have heard many things about there not being enough bandwidth over the network to stream a 20GB movie. Since this is going to be connected to my HTPC, I don't really need it to be connected to the network anyway.
I have an old Alienware from about 2003 laying around (Pentium 4, 1.5GB Ram, PCI, no sata) and I was thinking about getting a couple 4 port sata cards and putting 8 2TB drives in it.
Since it is going to be Direct attached I planned on using an esata cable or usb 3.0 (usb 3.0 would be preferred since i have usb 3.0 on my motherboard already)
It doesn't take a fast disk connection to "stream" a 20GB movie because the movie only "plays" at a transfer rate of a few MByte/sec. A slow connection may take a lot longer to copy the movie, but it will play the movie just as fast.
If you're taking about putting the drives into the same enclosure as your motherboard and SATA ports, that's no problem. But if you're talking about having a separate enclosure for the drives then the issue you'll face with eSATA will be the cable length limitation.
To avoid high power consumption, use "green" drives.
I highly recommend using a NAS for storing your movies. I built an unRAID server specifically for storing MKV files using software from Lime Technology. It works great and I use it to stream to my HTPC with XBMC (and other devices around the house).
Everything is running on a Gigabit network so there is plenty of bandwidth. Most MKV files are going to be under 10Mb/s. Even the maximum bitrate for a native Bluray is just under 50Mb/s which would stream fine on just 100Mbit Ethernet.
The unRAID array works a lot like a Drobo, in that it is easily expandable and energy efficient. UnRAID is pretty easy to configure and the Lime Technology support forums and community are very helpful. Disks in the unRAID array that aren't being used stay spun down which is not true on standard RAID setups. I've taken power measurements on my Atom based server (currently with 8 disks, all green drives) and it costs about $3.50-4.00 a month to keep up and running. UnRAID also uses a non-proprietary file system.
With unRAID you're going to get parity, so if a single drive fails, you won't lose data. You won't have that if you're thinking of using a JBOD setup.