Azure Storage Redundancy Explained

Storage redundancy questions appear frequently on AZ-900, and they're designed to test whether you understand what each option actually protects against — not just whether you've memorised the acronyms.

Locally-redundant storage (LRS) replicates your data three times within a single physical datacentre. It protects against hardware failure — a failed disk or server — but offers no protection if the entire datacentre goes offline.

Zone-redundant storage (ZRS) replicates your data across three availability zones within a single region. Availability zones are physically separate datacentres with independent power, cooling, and networking, so ZRS protects against a datacentre-level failure that LRS cannot survive.

Geo-redundant storage (GRS) replicates your data to a second, geographically distant paired region, in addition to the local redundancy in the primary region. This protects against a regional disaster — something that takes an entire region offline, which neither LRS nor ZRS can survive.

Geo-zone-redundant storage (GZRS) combines the two highest protection levels: zone-redundant storage in the primary region, plus geo-replication to a secondary region. This is the strongest protection Azure offers, surviving both a datacentre failure in the primary region and a full regional disaster.

The exam almost always signals which option is correct through specific language in the scenario. 'Survive a server failure' points to LRS. 'Survive a datacentre failure' or 'stay available if one building goes offline' points to ZRS. 'Survive a regional disaster' or 'a natural disaster affects the entire region' points to GRS or GZRS.