Great thank you. I'll continue to use the older AWS Glacier because the application still supports it after changing the config file to show all destination options.

Thanks David. It looks like the Synthetic Backup saves time and bandwidth by copying within the cloud storage account. When I noticed that there is a recommendation for periodic full backups, I got the impression that without a Synthetic Backup, the entire data set would need to be re-uploaded periodically. In many backup software, it doesn't do a scheduled full backup or require the user to manually refresh the full backup, it uploads a percentage of already backed up data along with the new data. That way over the course of a month, a full backup does exist. It's just made up of incremental backups throughout the month.

I'm backing up over a terabyte of photo files that are typically 35 MB each. The backups are being made in case of a drive failure or a once a year folder retrieval. It sounds like the backup software uploads archive files of X size containing partial file or multiple files depending on their size. With archive storage, block level changes can't be made and new blocks are uploaded to the storage rather than replacing blocks. Old blocks are automatically deleted depending on the retention policy.

It sounds like I should migrate my data from AWS Glacier to either the new S3 Glacier Deep Archive or Azure Archive.

And then for restoring a single file, does the application download a compressed file containing many files?