Storage Provisioning and Networking - Deploying and Managing a Cloud Infrastructure - page 264

Durability and Snapshots
Amazon EBS volumes are designed to be highly available and reliable. Amazon EBS volume
data is replicated across multiple servers in an Availability Zone to prevent the loss of data
from the failure of any single component. The durability of your volume depends both on the
size of your volume and the percentage of the data that has changed since your last snapshot.
As an example, volumes that operate with 20 GB or less of modified data since their most
recent Amazon EBS snapshot can expect an annual failure rate (AFR) of between 0.1 percent
and 0.5 percent (failure refers to a complete loss of the volume). This compares with com-
modity hard disks that will typically fail with an AFR of around 4 percent (as found by inde-
pendent studies from Google, Carnegie Mellon University, and University of Wisconsin at
Madison), making EBS volumes 10 times more reliable than typical commodity disk drives.
Replicating data across multiple volumes within the same Availability Zone provides only
a certain amount of durability. That is where point-in-time consistent snapshots of the vol-
umes play a part. Snapshots are stored in Amazon Simple Storage Serve (S3) cloud storage for
a nominal fee. The S3 automatically replicates the data volumes across multiple Availability
Zones. Taking regular snapshots is a convenient and cost-effective way to increase the long-
term durability of data. In the event of a volume failure, these snapshots will allow the user to
re-create the volume from the last available snapshot, thus minimizing the absolute data loss.

Amazon Simple Storage Service (S3)

Amazon S3 ( http://aws.amazon.com/s3/ ) is web-scale storage, which makes it easy for
the developers to store and retrieve data at any time and from anywhere on the Web. S3
provides a simple web services interface used for storing and retrieving vast amounts of
data. It is highly scalable, reliable, secure, and fast and is based on an inexpensive infra-
structure. Amazon uses S3 to run its network of websites.

Features
Amazon built S3 with a minimal feature set to have a generic base design. This enables it to
support various different objectives and otherwise conflicting requirements:

S3 can store an unlimited number of objects. These objects can be acted upon (read,
write, delete). Each object is stored in a bucket and assigned a unique key (required to
act upon the object). An object can contain data of anywhere between 1 byte and 5 TB.

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A bucket is stored in one of the several geographical regions. A region can be chosen
by the user for minimizing latency and costs and to conform to the address regulatory
requirements.

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Objects in a region stay in that region until explicitly transferred by the user. This
makes it easier for users to conform their services to international regulatory laws that
govern legal issues regarding IT (information technology), information, and data.

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Unauthorized access is blocked by standard authentication mechanisms. Objects can
also be made public or private. Moreover, rights can be granted to specific users.

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