Type of site
|Online backup service|
|Launched||August 21, 2012|
Glacier is part of the Amazon Web Services suite of cloud computing services, and is designed for long-term storage of data that is infrequently accessed and for which retrieval latency times of 3 to 5 hours are acceptable. Storage costs are a consistent $0.004 per gigabyte per month, which is substantially cheaper than Amazon's own Simple Storage Service (S3).
ZDNet says, that according to private e-mail, Glacier runs on "inexpensive commodity hardware components". In 2012, ZDNet quoted a former Amazon employee as saying that Glacier is based on custom low-RPM hard drives attached to custom logic boards where only a percentage of a rack's drives can be spun at full speed at any one time. (Similar technology is also used by Facebook.)
There is some belief amongst users that the underlying hardware used for Glacier storage is tape-based, owing to the fact that Amazon has positioned Glacier as a direct competitor to tape backup services (both on-premises and cloud-based). This confusion is exacerbated by the fact that Glacier has archive retrieval delays (3-5 hours before archives are available) similar to that of tape-based systems and a pricing model that discourages frequent data retrieval.
The Register claimed that Glacier runs on Spectra T-Finity tape libraries with LTO-6 tapes. Others have conjectured Amazon using off-line shingled magnetic recording hard drives, multi-layer Blu-ray optical discs, or an alternative proprietary storage technology.
While an unlimited amount of data can be uploaded for storage, the pricing structure for downloading data (retrieval) is far more complex. Getting data out of Glacier is a two-step process. The first step is to retrieve the data from Glacier staging area, subject to Glacier retrieval pricing. The next step is to actually download (transfer) the data. While Glacier advertises a free 5% per month allowance, this 5% is spread out evenly across the number of hours in a month for a 0.006944% free retrieval per hour (assuming a 30-day month). Exceeding the hourly allowance (aka peak hourly rate) at any time results in a peak retrieval overage charge that gets multiplied by the number of hours in a month.
In the more practical terms, Glacier users need to break up any sizeable retrievals across the longest period of time practical to eliminate or minimize overage charges. Developers who are planning to implement Glacier support in their applications also need to implement a mechanism for spreading out data retrieval over a long period of time, and to be extremely careful with their testing: a simple mistake or misunderstanding can easily result in a massive bill. In one example, a user stored 15 GB of data in Glacier, retrieved 693 MB for testing, and ended up being charged for 126 GB due to retrieval rate calculation.
Uploading data to Glacier is free, but downloading data from Glacier may be charged. This technically puts kind of a "time bomb" into data stored. Data transfer to the EC2 cloud in the same region is free, while data transfer between AWS regions is charged with $0.02 per GB ($0.09 per GB if data is downloaded from Tokyo region). Data transfer from Glacier to the Internet is free up to 1 GB per month, after which a sliding scale fee starts at $0.12 per GB. Data stored in Glacier but which is deleted after being stored for a period of less than 3 months incurs a charge of $0.03 per GB, a move designed to discourage the service's use in cases where Amazon's other storage offerings (e.g. S3) are more appropriate for real-time access.
Glacier is up to 66% cheaper than AWS S3, which in the past was the only way of archiving on the AWS cloud.
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