Storage Provisioning and Networking - Deploying and Managing a Cloud Infrastructure - page 252

it does come with a few difficulties. Failures are common among drives and are statistically
correlated. Unrecoverable read errors are among the most common problems and emanate
due to sector read failures. RAID-6, with a double protection scheme, addresses this issue
but pays the penalty in very high disk I/O (writing) time.
Moreover, due to nonatomicity of data and therefore inconsistency arising from random
system crashes, parity and data are left in an inconsistent state.
Cloud storage uses version copies, which makes it highly durable. Atomicity of operations
in the cloud environment ensures that the data is in one consistent state (before committing
the transaction) or another (after successfully committing the transaction). Moreover, in the
event of failures, a cloud system is guaranteed to reach a consistent state eventually (called
eventual consistency ) with regard to the data replicas. Eventual consistency informally
guarantees that if no new updates are made to a given data item (which is replicated to vari-
ous locations), eventually all access to that item will return the last updated value. This is
because the data item will eventually be “updated” at every location with the latest value.
Advantages of Cloud Storage
Cloud storage also offers a number of advantages over an onsite data store setup such as a
SAN. For instance, companies using the cloud storage services need to pay only for the storage
they actually use. This not only means a lower operating expense, it also avoids capital expen-
diture and maintenance costs.
Moreover, storage availability and data protection are intrinsic to object storage archi-
tecture. Cloud storage also provides users with a broad range of applications and resources
as part of the service provider's infrastructure.
However, not all is well in the world of cloud storage. If care is not taken for a few but
important factors, cloud storage could become a great concern, especially for organizations
for which data translates to money. These concerns include attack surface area, supplier
stability, accessibility, security, and privacy and are addressed in detail in the section “Cloud
Security and Privacy” later in this chapter.
Cloud Provisioning
For companies making the transition, there are some big business and administrative questions
to answer. Companies are not only thinking about the costs and flexibility of technological
operations, they're also thinking of tactical advantages like automated provisioning (of virtual
resources and services) and encrypted storage.
This administrative and technological conundrum of the extent and procedures of tran-
sition is what cloud provisioning entails. Companies need to decide what part of their infra-
structure goes into the cloud as a part of their cloud computing strategy. They also need to
see whether to have segregation between a privately deployed cloud infrastructure and the
public cloud.