Echthros

"First: Totally forget about HFS, exFAT, etc, support. The NAS will be sharing the files over SMB or NFS, both of which macOS can connect to with no problems. The local filesystem of the NAS is irrelevant, since the network protocol (SMB) will translate everything for you."
 
That's good to get a clear answer on. I was having trouble getting clarity on different forums I was looking in (probably because just mentioning Apple and NAS in Google automatically assumes I'm trying to use a NAS as a Time Machine target location... which I'm not. And everyone Apple seems to just default to "Use HFS+ always").
 
"But remember, RAID is NOT a backup solution, It protects against hardware failure, but not against data loss resulting from accidental deletion (Eg: If someone deletes the Library folder by accident, the NAS will automatically replicate that deletion to the 2nd mirrored drive), or virus infection, etc."
 
I understand that RAID is not the backup solution for the iTunes library. Part of the reason why I've been digging into this is that the 8 year old iMac the library is currently on is starting to show signs of it's age in that accessing the data on the HDD is getting slower (whether that's due to the HDD or the other hardware isn't clear but I want to avoid a HDD failure at this point.) Music is generally "backed up" to my Google Play account. Getting a local backup is there to avoid having to re-download all the music in case of hardware failure *in addition* to providing storage separate from the MBP. 
 
Thanks for the feedback. Synology looks solid. I'll see what cash comes in next month to try and get this started. I may try to scrounge an external drive from one of our dads' stashes (both have worked in large-scale IT for years so they always have vendor swag laying around) to hang off the router in HFS+ to hold the iTunes library temporarily so I can decommission the iMac and get the cash to do the NAS right.

"First: Totally forget about HFS, exFAT, etc, support. The NAS will be sharing the files over SMB or NFS, both of which macOS can connect to with no problems. The local filesystem of the NAS is irrelevant, since the network protocol (SMB) will translate everything for you."
 
That's good to get a clear answer on. I was having trouble getting clarity on different forums I was looking in (probably because just mentioning Apple and NAS in Google automatically assumes I'm trying to use a NAS as a Time Machine target location... which I'm not. And everyone Apple seems to just default to "Use HFS+ always").
 
"But remember, RAID is NOT a backup solution, It protects against hardware failure, but not against data loss resulting from accidental deletion (Eg: If someone deletes the Library folder by accident, the NAS will automatically replicate that deletion to the 2nd mirrored drive), or virus infection, etc."
 
I understand that RAID is not the backup solution for the iTunes library. Part of the reason why I've been digging into this is that the 8 year old iMac the library is currently on is starting to show signs of it's age in that accessing the data on the HDD is getting slower (whether that's due to the HDD or the other hardware isn't clear but I want to avoid a HDD failure at this point.) Music is generally "backed up" to my Google Play account. Getting a local backup is there to avoid having to re-download all the music in case of hardware failure *in addition* to providing storage separate from the MBP. 
 
Thanks for the feedback. Synology looks solid. I'll see what cash comes in next month to try and get this started. I may try to scrounge an external drive from one of our dads' stashes (both have worked in large-scale IT for years so they always have vendor swag laying around) to hang off the router in HFS+ to hold the iTunes library temporarily so I can decommission the iMac and get the cash to do the NAS right.