Unlike S3, Amazon's Glacier service does not offer immediate download (restore). When restoring from Glacier, Arq must first request that the objects be made downloadable. This takes approximately 1-5 minutes (Expedited retrieval tier), 3-5 hours (Standard retrieval tier) or 5-12 hours (Bulk retrieval tier).. Once the objects are downloadable, Arq downloads them.
When you click "Restore", Arq begins requesting objects, and continues until it has requested the amount of data that would take 4 hours for example (for Standard tier) to download at the rate you’ve chosen. After 4 hours have elapsed, it begins requesting another 4 hours’ worth of objects, and simultaneously begins downloading objects that are becoming available. It continues this pattern until all the files have been downloaded.
(The following pricing numbers are based on the Amazon "US East" region.)
Calculating pricing for downloading your data from Glacier can be confusing.
Restoring a file from Glacier is a 3-step process. First you issue a Glacier restore request for an object. Then you wait approximately 4 hours for the object to become available for download. Then you download it.
You can restore up to 5% of your Glacier data for free each month, prorated daily. For example, if you’ve backed up 100GB of files to Glacier, you can restore 5GB for free each month — 160MB each day.
As of 21 November, 2016, Amazon has simplified their pricing for retrieving data from Glacier. You pay a flat per-GB rate for the data you retrieve. The rate depends on which tier you've chosen -- Bulk, Standard or Expedited.
You'll also pay a "data transfer out" fee per GB downloaded.
Arq estimates these costs for you before you start the restore process.