The Wiki site gives the space efficiencies. For RAID 6 it quotes 1-2/n which, for a four drive array, equals 0.5 (or 50%). Not surprising as the ability to lose two drives with no loss of data means that all the data must be storable on the two remaining drives. My very personal take on this is that RAID 6 is too much of a good thing and that RAID 5 is good enough for a home NAS box. It's pretty unlikely that you'll lose a second hard drive before you have a chance to replace a failed drive and let the NAS rebuild the array and it still doesn't make sense for any NAS to be the only backup solution deployed, particularly for critical data.
To give my own NAS setup as an example, it supplies online backup for my main PC, it also provides "always available" storage for my Media Center files (a lot
of data) and provides a convenient way to transfer files between PCs when the target PC isn't switched on. But, and it's a big "but" IMHO, I also make Windows backups to an external HDD, albeit far less frequently than my daily ones to the NAS courtesy of SFFS
, and I store the external HDD in a fire safe. All of my media files are also backed up onto a couple of external HDDs, not because I couldn't recreate them if disaster struck but simply because it would take months
of work to do so.
This may seem to be a bit over the top but with the cost per gigabyte of external drives being so reasonable these days it's a relatively low premium to pay for a significant extra layer of data security while still retaining the convenience of a 24/7 NAS solution which, by the very nature of it always being switched on, does run a tiny risk of losing all the data stored on it due, for instance, to a major voltage spike (e.g. lightning) frying all the electronics including possibly the individual hard drives.
As for noise, I could
live with my QNAP TS-639 Pro (now replaced I believe by the TS-659 Pro
) in the office. That's not
something I could have said for any of the LaCie units I previously employed but as I had already made the investment of adding a suitably run of "gigabit" Ethernet cabling it made good sense to keep my NAS in an outbuilding.