Just today finally got around to creating a fresh backup, and it's slower than I seem to recall. I know routine backups are 'incremental' and now I am doing a new one, but 2 hours in only about 10% of the way there (10% of 500 albums). Does that seem right on a gigabit network? Must take days for folks with really large libraries!
What are you backing up to ? The write speed of the receiving device plays quite a part in timing.
Internal HDD seems quickest followed by USB3.0 Ext HDD.
I've always done my backups to an external drive, although in the past it was a drive directly connected via USB2.0 to my computer, whereas this time I'm making a redundant copy to my Raid1 NAS. You're likely right that it is the destination device (didn't occur to me until you pointed it out).
It would be best if ALL Components involved in the Backup are on the Wired Gigabit Network...........i.e. the Sooloos Storage, the NAS Backup and the PC doing the Backup Routine
Having the PC on Wifi will slow down the Backup significantly........as will essentially writing to the Two Disks involved in your NAS Raid 1
I have also backed up to my NAS (Raid5) and it took about 5 or 6 days !!!! (100k tracks)
The same library to a USB 3.0 HDD via a USB 3.0 port was about 1.5 days.
I now copy a native export internal HDD back to the NAS from PC which is pretty quick. So, it seems that keeping the data routing simple for C-PC works best.