All charges incurred stay between you and S3; Haystack Software never sees your data or your billing. The backups use an open documented format with encryption that you control. You can even grab individual files from your backups on-the-go using the free iOS client.
Now, Arq has added support for Amazon Glacier. A lower-cost alternative to S3, Glacier lets you store data at a fraction of the price, e.g. $0.01/GB/month vs $0.125/GB/month. (These rates do vary somewhat based on bulk use and other factors.)
Glacier was designed for rarely accessed data with flexible retrieval times. Instead of instant access, you request a "job" that typically completes within a few hours. This allows Amazon to trade-off access loads for price. You pay less but you may have to wait for your data.
This makes Glacier the perfect budget solution for items that you want protected but that you rarely access such as baby pictures, old blog archives, completed work projects and so forth.
You choose the destination for each folder you back up, selecting either S3 or Glacier. Arq's backup set list indicates where each item get backed up to. Here, the destination for this iPhoto library is Glacier.
Arq provides incremental backup support, only updating changes like Time Machine does. It runs a background daemon that monitors the folders you've selected.
Overall, you choose whether to back up every hour or every day. From your point of view, there's no real difference in backing up to S3 or Glacier. You simply choose which destination you wish to use.
Arq and Your Budget
Arq is sensitive to your budget needs for both S3 and Glacier backups, providing excellent consumer feedback and planning. For S3, you tell it how much you wish to spend per month on data storage. Arq trims away older backup versions to stay within that budget. With Glacier, you choose when and how to download data back from the Amazon servers so your expenditures stay low.
You don't specify an exact budget number with Glacier the way you do with S3, and there's a couple of reasons for that. First of all, Glacier is way cheaper overall. So there's not as much of a compelling motivation for enforcing stored-data limits the way you do with S3 in Arq. You can send up a lot more data and it's not going to kill you financially. Second, Glacier imposes early deletion penalties that can add unneeded costs to your monthly bill. Arq knows that you'll want to avoid that.
For Glacier, instead, you budget by choosing how quickly you want to restore. Glacier uses a tiered retrieval fee. You pay based on your peak hourly retrieval rate over a month. If you need data fast, you pay for it. So Arq lets you tweak your download speed to limit how much this fee will be. Lower the speed and your retrieval fee for the month goes down as well.
Tiered retrieval fees don't apply to S3. With S3, you can grab data whenever and however you need it. Your costs reflect standard S3 data transfer rates. You may restore on a file-by-file basis or recover entire folders.
Arq's 3.0 update is a terrific addition to an already excellent tool. If you haven't already checked out Arq, you can test it out free for 30 days. It offers a great "bring your own storage" solution that leverages Amazon's S3 and Glacier web services.
Glacier support is now live. Existing users can upgrade to 3.0 through a $15 in-app upgrade. Choose "Check for Updates" from the Arq menu.