Cut cost by what?
I run a 14 terabyte raid at my house... The total cost of the unit was about $1500 and that was long ago. I can mirror the RAID with rsync (or equivalent) to another location quite easily providing 100% redundancy. I can replace the drives in the mirror with 4tb drives instead of 2tb drives and even have revisioning.
The cost of running the system is painfully low... the machine has a total average power consumption of 27 watts and successfully floods the three internal gigabit ethernet adapters. The precise same computer build has been used for full 4K video production on 5 Avid, Final Cut Pro and Adobe workstations where non-linear editing was performed without a hiccup.
Could I implement the same tech on a large scale (petabytes a dozens of gigabit ethernet links)? sure... no problem. I could easily scale this tech to petabytes or tens of petabytes with full redundancy. Mirroring would even be easy using point to point 10Gbe adapters. The trick is simply using file systems which support distribution.
Tape technology is nice, but it's way too small, way too slow and way too unreliable. Yes, unreliable. Tape is a shitty solution these days. You're making use of an insanely long strip of magnetic media which is being spun in layers in a harsh environment around a spool and then transported to a "safe place". Error detection and correction improves it a bit, but the bit density of tape is just too high to reliably store media as such... therefore you need multiple tapes of the same data.
It's just too slow and too unreliable for modern use. Multi-location raids are far more reliable and, if implemented correctly, power friendly. It's also substantially faster.
My dream at the moment is a single board computer with a ULV Core i5 (such as those in tablets), 16GByte soldered on ULV DDR3, 4 accelerated Gigabit ethernet ports (including jumbo packet support and IPv6 TCP/UDP checksum calculation) and a soldered on HighPoint-Tech 8-port SAS 6Gbit controller with support for SAS expanders. Oh... and full support for low power on all accessories when idle. A soldered on 128Gb boot drive would also be awesome.
A board like this would probably have an average power consumption of 8watts. It would peak around 40. Using 5400RPM drives with this board would have an average power consumption of well under 2 watts per drive each.
There's no point wasting time with a multicore ARM processor as nearly all the power is likely consumed by the peripherals and frankly, unless highpoint makes their own ARM cpu, it's almost certainly going to be some shit controller from some lame ass ARM company who focused more on the ARM than on the RAID.