Storage Replication Flashcards
What is LRS? Describe it.
Data in an Azure Storage account is always replicated three times in the primary region. Azure Storage offers two options for how your data is replicated in the primary region:
Locally redundant storage (LRS) copies your data synchronously three times within a single physical location in the primary region. LRS is the least expensive replication option, but isn’t recommended for applications requiring high availability or durability.
What is ZRS? Describe it.
Data in an Azure Storage account is always replicated three times in the primary region. Azure Storage offers two options for how your data is replicated in the primary region:
Zone-redundant storage (ZRS) copies your data synchronously across three Azure availability zones in the primary region. For applications requiring high availability, Microsoft recommends using ZRS in the primary region, and also replicating to a secondary region.
What is Locally Redundant Storage?
Locally redundant storage (LRS) replicates your storage account three times within a single data center in the primary region. LRS provides at least 99.999999999% (11 nines) durability of objects over a given year.
LRS is the lowest-cost redundancy option and offers the least durability compared to other options. LRS protects your data against server rack and drive failures. However, if a disaster such as fire or flooding occurs within the data center, all replicas of a storage account using LRS may be lost or unrecoverable. To mitigate this risk, Microsoft recommends using zone-redundant storage (ZRS), geo-redundant storage (GRS), or geo-zone-redundant storage (GZRS).
A write request to a storage account that is using LRS happens synchronously. The write operation returns successfully only after the data is written to all three replicas.
The following diagram shows how your data is replicated within a single data center with LRS:
https://learn.microsoft.com/en-us/azure/storage/common/media/storage-redundancy/locally-redundant-storage.png
When is LRS a good choice?
o If your application stores data that can be easily reconstructed if data loss occurs, you may opt for LRS.
o If your application is restricted to replicating data only within a country or region due to data governance requirements, you may opt for LRS. In some cases, the paired regions across which the data is geo-replicated may be in another country or region. For more information on paired regions, see Azure regions.
o If your scenario is using Azure unmanaged disks, you may opt for LRS. While it’s possible to create a storage account for Azure unmanaged disks that uses GRS, it isn’t recommended due to potential issues with consistency over asynchronous geo-replication.
What is Zone Redundant Storage (ZRS)
Zone-redundant storage (ZRS) replicates your storage account synchronously across three Azure availability zones in the primary region. Each availability zone is a separate physical location with independent power, cooling, and networking. ZRS offers durability for storage resources of at least 99.9999999999% (12 9’s) over a given year.
With ZRS, your data is still accessible for both read and write operations even if a zone becomes unavailable. If a zone becomes unavailable, Azure undertakes networking updates, such as DNS repointing. These updates may affect your application if you access data before the updates have completed. When designing applications for ZRS, follow practices for transient fault handling, including implementing retry policies with exponential back-off.
A write request to a storage account that is using ZRS happens synchronously. The write operation returns successfully only after the data is written to all replicas across the three availability zones.
Microsoft recommends using ZRS in the primary region for scenarios that require high availability. ZRS is also recommended for restricting replication of data to a particular country or region to meet data governance requirements.
Microsoft recommends using ZRS for Azure Files workloads. If a zone becomes unavailable, no remounting of Azure file shares from the connected clients is required.
The following diagram shows how your data is replicated across availability zones in the primary region with ZRS:
https://learn.microsoft.com/en-us/azure/storage/common/media/storage-redundancy/zone-redundant-storage.png
ZRS provides excellent performance, low latency, and resiliency for your data if it becomes temporarily unavailable. However, ZRS by itself may not protect your data against a regional disaster where multiple zones are permanently affected. For protection against regional disasters, Microsoft recommends using geo-zone-redundant storage (GZRS), which uses ZRS in the primary region and also geo-replicates your data to a secondary region.
The Archive tier for Blob Storage isn’t currently supported for ZRS, GZRS, or RA-GZRS accounts. Unmanaged disks don’t support ZRS or GZRS.
For more information about which regions support ZRS, see Azure regions with availability zones.
What are the standard storage accounts>
Standard storage accounts
ZRS is supported for all Azure Storage services through standard general-purpose v2 storage accounts, including:
o Azure Blob storage (hot and cool block blobs and append blobs, non-disk page blobs)
o Azure Files (all standard tiers: transaction optimized, hot, and cool)
o Azure Table storage
o Azure Queue storage
How does Redundancy in a secondary region work?
For applications requiring high durability, you can choose to additionally copy the data in your storage account to a secondary region that is hundreds of miles away from the primary region. If your storage account is copied to a secondary region, then your data is durable even in the case of a complete regional outage or a disaster in which the primary region isn’t recoverable.
When you create a storage account, you select the primary region for the account. The paired secondary region is determined based on the primary region, and can’t be changed. For more information about regions supported by Azure, see Azure regions.
Azure Storage offers two options for copying your data to a secondary region:
o Geo-redundant storage (GRS)
o Geo-zone-redundant storage (GZRS)
What is Geo-redundant storage (GRS) ?
Geo-redundant storage (GRS) copies your data synchronously three times within a single physical location in the primary region using LRS. It then copies your data asynchronously to a single physical location in the secondary region. Within the secondary region, your data is copied synchronously three times using LRS.
Note
The primary difference between GRS and GZRS is how data is replicated in the primary region. Within the secondary region, data is always replicated synchronously three times using LRS. LRS in the secondary region protects your data against hardware failures.
With GRS or GZRS, the data in the secondary region isn’t available for read or write access unless there’s a failover to the primary region. For read access to the secondary region, configure your storage account to use read-access geo-redundant storage (RA-GRS) or read-access geo-zone-redundant storage (RA-GZRS). For more information, see Read access to data in the secondary region.
If the primary region becomes unavailable, you can choose to fail over to the secondary region. After the failover has completed, the secondary region becomes the primary region, and you can again read and write data. For more information on disaster recovery and to learn how to fail over to the secondary region, see Disaster recovery and storage account failover.
Important
Because data is replicated to the secondary region asynchronously, a failure that affects the primary region may result in data loss if the primary region cannot be recovered. The interval between the most recent writes to the primary region and the last write to the secondary region is known as the recovery point objective (RPO). The RPO indicates the point in time to which data can be recovered. The Azure Storage platform typically has an RPO of less than 15 minutes, although there’s currently no SLA on how long it takes to replicate data to the secondary region.
What is Geo-zone-redundant storage (GZRS)?
Geo-zone-redundant storage (GZRS) copies your data synchronously across three Azure availability zones in the primary region using ZRS. It then copies your data asynchronously to a single physical location in the secondary region. Within the secondary region, your data is copied synchronously three times using LRS.
Note
The primary difference between GRS and GZRS is how data is replicated in the primary region. Within the secondary region, data is always replicated synchronously three times using LRS. LRS in the secondary region protects your data against hardware failures.
With GRS or GZRS, the data in the secondary region isn’t available for read or write access unless there’s a failover to the primary region. For read access to the secondary region, configure your storage account to use read-access geo-redundant storage (RA-GRS) or read-access geo-zone-redundant storage (RA-GZRS). For more information, see Read access to data in the secondary region.
If the primary region becomes unavailable, you can choose to fail over to the secondary region. After the failover has completed, the secondary region becomes the primary region, and you can again read and write data. For more information on disaster recovery and to learn how to fail over to the secondary region, see Disaster recovery and storage account failover.
Important
Because data is replicated to the secondary region asynchronously, a failure that affects the primary region may result in data loss if the primary region cannot be recovered. The interval between the most recent writes to the primary region and the last write to the secondary region is known as the recovery point objective (RPO). The RPO indicates the point in time to which data can be recovered. The Azure Storage platform typically has an RPO of less than 15 minutes, although there’s currently no SLA on how long it takes to replicate data to the secondary region.
What is geo-gedundant Storage and how does it work?
Geo-redundant storage (GRS) copies your data synchronously three times within a single physical location in the primary region using LRS. It then copies your data asynchronously to a single physical location in a secondary region that is hundreds of miles away from the primary region. GRS offers durability for storage resources of at least 99.99999999999999% (16 9’s) over a given year.
A write operation is first committed to the primary location and replicated using LRS. The update is then replicated asynchronously to the secondary region. When data is written to the secondary location, it’s also replicated within that location using LRS.
The following diagram shows how your data is replicated with GRS or RA-GRS:
https://learn.microsoft.com/en-us/azure/storage/common/media/storage-redundancy/geo-redundant-storage.png
What is geo-zone-redundant storage and how does it work?
Geo-zone-redundant storage (GZRS) combines the high availability provided by redundancy across availability zones with protection from regional outages provided by geo-replication. Data in a GZRS storage account is copied across three Azure availability zones in the primary region and is also replicated to a secondary geographic region for protection from regional disasters. Microsoft recommends using GZRS for applications requiring maximum consistency, durability, and availability, excellent performance, and resilience for disaster recovery.
With a GZRS storage account, you can continue to read and write data if an availability zone becomes unavailable or is unrecoverable. Additionally, your data is also durable in the case of a complete regional outage or a disaster in which the primary region isn’t recoverable. GZRS is designed to provide at least 99.99999999999999% (16 9’s) durability of objects over a given year.
The following diagram shows how your data is replicated with GZRS or RA-GZRS:
https://learn.microsoft.com/en-us/azure/storage/common/media/storage-redundancy/geo-zone-redundant-storage.png
Only standard general-purpose v2 storage accounts support GZRS. GZRS is supported by all of the Azure Storage services, including:
Azure Blob storage (hot and cool block blobs, non-disk page blobs)
Azure Files (all standard tiers: transaction optimized, hot, and cool)
Azure Table storage
Azure Queue storage
How many copies of data in LRS?
Three copies within a single region.
How many copies of data in ZRS?
Three copies across separate availability zones within a single region.
What is an Azure Availability Zone?
Azure Availability Zones is a high-availability offering that protects your applications and data from datacenter failures.
These are unique physical locations within an Azure region. Each zone is made up of one or more data centers equipped with independent power, cooling, and networking.
The physical separation of Availability Zones within a region protects applications and data from datacenter failures.
Zone-redundant services replicate your applications and data across Azure Zones to protect from single-points-of-failure.
Not every region has support for Availability Zone Azure. The examples of Availability Zones are Central US, East US 2, West US 2, West Europe, France Central, North Europe & Southeast Asia
With Availability Zones, Azure offers industry best 99.99% VM uptime SLA(Service Level Agreement)
https://k21academy.com/wp-content/uploads/2020/03/0207.AvailabilityZone.png-550x0.png
What is change feed?
The purpose of the change feed is to provide transaction logs of all the changes that occur to the blobs and the blob metadata in your storage account. The change feed provides ordered, guaranteed, durable, immutable, read-only log of these changes. Client applications can read these logs at any time, either in streaming or in batch mode. The change feed enables you to build efficient and scalable solutions that process change events that occur in your Blob Storage account at a low cost.
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