Which feature(s) ensures that the stored content has NOT been altered in a CAS system?

A.
Single instance storage

B.
Content integrity

C.
Content mirroring and parity protection

D.
Location independence

Explanation:
Key features of CAS
CAS provides all the features required for storing fixed content. The key features of CAS are as
follows:
• Content authenticity: It assures the genuineness of stored content. This is achieved by
generating a unique content address for each object and validating the content address for stored
objects at regular intervals. Content authenticity is assured because the address assigned to each
object is as unique as a fingerprint. Every time an object is read, CAS uses a hashing algorithm to
recalculate the object’s content address as a validation step and compares the result to its original
content address. If the object fails validation, CAS rebuilds the object using a mirror or parity
protection scheme.
• Content integrity: It provides assurance that the stored content has not been altered. CAS uses a
hashing algorithm for content authenticity and integrity. If the fixed content is altered, CAS
generates a new address for the altered content, rather than overwrite the original fixed content.
• Location independence: CAS uses a unique content address, rather than directory path names
or URLs, to retrieve data. This makes the physical location of the stored data irrelevant to the
application that requests the data.
• Single-instance storage (SIS): CAS uses a unique content address to guarantee the storage of
only a single instance of an object. When a new object is written, the CAS system is polled to see
whether an object is already available with the same content address. If the object is available in
the system, it is not stored; instead, only a pointer to that object is created.
• Retention enforcement: Protecting and retaining objects is a core requirement of an archive
storage system. After an object is stored in the CAS system and the retention policy is defined,
CAS does not make the object available for deletion until the policy expires.
• Data protection: CAS ensures that the content stored on the CAS system is available even if a
disk or a node fails. CAS provides both local and remote protection to the data objects stored on it.
In the local protection option, data objects are either mirrored or parity protected. In mirror
protection, two copies of the data object are stored on two different nodes in the same cluster.
This decreases the total available capacity by 50 percent. In parity protection, the data object is
split in multiple parts and parity is generated from them.
Each part of the data and its parity are stored on a different node. This method consumes less
capacity to protect the stored data, but takes slightly longer to regenerate the data if corruption of
data occurs. In the remote replication option, data objects are copied to a secondary CAS at the
remote location. In this case, the objects remain accessible from the secondary CAS if the primary
CAS system fails.
• Fast record retrieval: CAS stores all objects on disks, which provides faster access to the objects
compared to tapes and optical discs.
• Load balancing: CAS distributes objects across multiple nodes to provide maximum throughput
and availability.
• Scalability: CAS allows the addition of more nodes to the cluster without any interruption to data
access and with minimum administrative overhead.
• Event notification: CAS continuously monitors the state of the system and raises an alert for any
event that requires the administrator’s attention. The event notification is communicated to the
administrator through SNMP, SMTP, or e-mail.
• Self diagnosis and repair: CAS automatically detects and repairs corrupted objects and alerts the
administrator about the potential problem. CAS systems can be configured to alert remote support
teams who can diagnose and repair the system remotely.
• Audit trails: CAS keeps track of management activities and any access or disposition of data.
Audit trails are mandated by compliance requirements.
EMC E10-001 Student Resource Guide. Module 8: Object-based and Unified Storage