Q53 : Why is replication important? How many options are available for replicating data in your storage account?

Replication ensures durability and also highly availability of your data.

There are several ways you can replicate data.

Locally redundant storage (LRS)
Zone-redundant storage (ZRS)
Geo-redundant storage (GRS)
Read-access geo-redundant storage (RA-GRS)

LRS refers to storing copies of data in the same facility of the same region. The copies are stored in separate fault domains and upgrade domains. This ensures that the data is available even when a storage node fails.

When data is being updated, update requests are sent to all three copies and only when this is successful the updated operation is deemed successful. This ensures that all three copies of data are in sync.

GRS refers to storing three copies of LRS copies in the primary region. The primary region is chosen by the account holder and ensures that copies of data are always available. Note that each region has a Microsoft’s specified associated primary region. In case of a failure, Microsoft will enable the GRS copies to be available.

Read-Access Geo-Redundant Storage (RA-GRS)

When a subscriber chooses this option, he can read the data in the secondary region. This feature is an improvement to the GRS.

Zone Redundant Storage (ZRS)

This feature is applicable only to Block Blob storage and is not applicable to other blob storage which is the page blobs. When this feature is enabled, data is replicated across three facilities.
Microsoft recommends GRS replication option for providing maximum durability for your data.