For about $1000, you can now buy a 26 TB HD optimized for NAS use. With RAID 6 (which tolerates the loss of up to 2 disks) on a 6 disk NAS, that's a capacity of 104 TB. I now have mine for about 10 years. 6x6 TB, that's 36TB-12, so 24 TB available capacity. I fortunately don't need 100 TB, but an upgrade to 30 TB would be nice - and much cheaper.