The only thing I’d add to this is that I use USB drives for backup. They’re stored in different places in the house including a 60 minute fireproof box (a long time ago I gave a backup to someone that’s off site - I really ought to do that again!). I always let the backup drives warm up for 24 hours before using them.
My main storage is on a Melco Raid 1 server.
@Carousel I do just what you said “pass stereo DSD from my NAS to my PS Audio DAC via I2S HDMI.” It requires a few boxes and Roon. I have a Sonore Streamer with USB to Matrix SPDIF2 which then sends I2S to Directstream DAC. Found this better than the Bridge. It does all things Stereo. Even down converts mulit channel FLAC to 2 channel. For surround music I have my oppo read from the NAS and use it as the controller. Again, requires roon or some other streaming software, but there are many many simple streamers out there that can output USB and the Matrix is pretty cheap to make it I2S.
All good points. In IT we have two concepts: Redundancy and Backup
Redundancy is making sure that whatever system is in place doesn’t have a single point of failure. In MikeK’s example, and they used the term correctly, a Synology NAS provides redundancy in that any single disk can fail and your data is still good (there are more sophisticated systems that can handle multiple disk failures). It’s nice to have redundancy so, inevitably, when a disk holding your music fails at 6PM on a Friday you can still listen to and not have to worry about it until Monday. But, redundancy in the some is usually less important than having a proper backup.
Backups are to protect against data loss when the storage system fails. That is, if the entire Synology array were to fail. At that point, you need a backup to restore the data. Backups can also help in situations of catastrophic failure of location, like the building where the Synology lives no longer existing, and that’s where cloud backups can be really nice. The other reason for having proper backups is data corruption. Redundant systems provide 1 copy of your data. If that copy is corrupted redundancy just maintains the corruption. A proper backup, or multiple backups, let you go back in time to restore a sane copy of the data.
Anyway, don’t confuse redundancy for a backup (lots of people do) and always make sure you’ve got a true backup of the data in case of failure within your storage systems.
@MikeK Your two systems sound excellent in that they both provide redundancy and the smaller array is a great backup to your larger one.
That’s about as simple as secure backups get. Even I could follow those directions!
I don’t use cloud storage for anything just for the reasons you stated.
Unfortunately for me I have to have all of my machines at work connected to the internet. We use it as a main source of file transfers back and forth between customers and our shop.
It worries me a little every day.
I’m a novice too. How do you back up SACD’s? They are all hybrids. I’ve been using iTunes for backing up all my CDs but I know it will not cover the SACD portion.
I have all my SACDs backed up from the NAS along with every other format Disc. I plug a usb hard drive into the nas and used the on board back up plugin that keeps it up to date. But you have to rip the SACDs to files first.
There’s a section on this subject.
See How Do You Rip SACD’s
I only backup my MP3s. They’re saved on various 1TB thumb drives, strewn here and about. Some in other countries and what not.
Yes it is and I use it for the occasional back-up using a WD HDD. Presently my Innuos drive is full. I am on the fence regarding expanding internal storage, a major PITA as it must be shipped to Portugal, or adding a separate NAS which I’d rather not due as I don’t like the idea of additional wires, boxes, etc.
A little bit of paranoia is not unhealthy… 
I just use 4TB USB drives, and I have four of them that are strictly backups. None are connected except when I’m adding new files to them, and one is always in my safe deposit box at the bank (rotated every few weeks). Another is in my gun safe, which is rated for 60 minutes fireproof at 1200 degrees.
If I somehow lost all 4 drives simultaneously, I’m pretty sure whatever does it will take me out as well, at which point I no longer care. 
Well put ipeverywhere and I appreciate your gentle reminder of the important distinction between ‘redundancy’ and ‘backup’. 
It influences me to implement a true backup strategy for my library. 
BTW, thanks to @Elk for splitting off this topic from the AirLens discussion. It was threatening to greatly sidetrack things. 
I regret retiring my DAT.
I almost completely forgot about tape backups.
With larger hard drive and SSD drive capacity tape became less cost effective.
I did like DAT once it was setup. Especially since I did full every time. It was easy to rotate. The final version of Veritas was quite good.
I have an 8mm tape drive here somewhere… I’m not entirely sure I have a functioning machine to put it in.
I don’t have the five or six various tape drives I once used. But I do have the tapes. Why though? LOL.
I assume there’s a service out there that’s basically the Smithsonian of Compute and there’s a little bit of everything available…for a choice fee.
I imagine there’s a VAX 8600 available just waiting for us to do a restore that saves earth from annialation.
Don’t forget, “Even paranoids have enemies”.
Hey I still have a Tascam DA-20 MkII DAT machine. If you want to make some room by getting rid of those tapes I will certainly welcome them…