Arq does not seem to be in the same ballpark as Deep Archive with regards to pricing. Also I needed a Linux solution, they support Win/Mac only unfortunately (same as Backblaze).
I'm confused by this comment. Arq can store your backups in your own AWS account, using Glacier Deep Archive storage class. It's your own AWS account, so you pay exactly the Deep Archive price.
I understand, didn't see this mentioned on the pricing page directly. How do they store the data in Deep Glacier (single files or archives? the former would be very expensive?) Do they have restore fully integrated? (since this is a two-step process that takes 12+ hours I could imagine it does not fit the normal flow)
Arq manages the restore process, telling AWS to make Glacier/Deep Archive objects "downloadable", waiting for them to become downloadable, and then downloading the data.
Arq is a GUI client that stores your backups in the location you set it up for. See screenshot in the "Back up to your own cloud account." section on https://www.arqbackup.com.
