I built my own, use XigmaNAS and RaidZ3 across 15 2TB disks for 22TB usable. Backup is now my main PITA - I lost a previous array with RaidZ2 by losing 3 disks trying to rebuild, so while I should have known better, RAID is not a backup. However, finding large external disks with any sort of reliability seems hard - so many bad reviews of 12TB etc disks. For now, I'm actually only using about 3.2TB and so can backup to jottacloud, but it's slow with my internet. I think the first full backup tool 3 months or something. Luckily I use something that is all incremental after that, but I probably actually need to set up a 20TB disk or something to just make full copies over to occasionally.