EBS asynchronously replicates disk data from a primary site to a secondary site across zones or regions, enabling failover when the primary site fails.
Use cases
Disk disaster recovery covers two scenarios:
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Cross-zone disaster recovery: Recover from zone-level failures such as data center fires, blackouts, or device faults.
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Cross-region disaster recovery: Protect against regional disasters such as earthquakes or tsunamis by failing over to a secondary site in a different region.
Features
EBS provides two disaster recovery features based on the number of disks involved.
Async replication
Async replication provides disaster recovery for a single disk set. It asynchronously replicates data from a primary disk to a secondary disk in a different region or zone. If the primary disk fails, you can fail over to the secondary disk and perform a reverse replication.
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Cross-zone disaster recovery
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Cross-region disaster recovery
Replication pair-consistent group
A replication pair-consistent group provides disaster recovery for multiple disk sets. It lets you batch manage disks in scenarios where a business system spans multiple disks, restoring all disks to the same point in time.
Data is asynchronously replicated from primary disks to secondary disks across regions or zones. When the primary site fails, you can fail over to the secondary site and perform a reverse replication.
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Cross-zone disaster recovery
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Cross-region disaster recovery
Limitations
Specification limits
The following table lists specification limits for async replication and replication pair-consistent groups.
|
Item |
Limit |
|
Replication pairs per disk |
1 |
|
Replication pairs per replication pair-consistent group |
17 |
|
Replication cycle |
15 minutes |
|
Replication rate |
Up to 100 MB/s. Varies based on system load. |
|
Primary disk category |
ESSD or ESSD AutoPL disks |
|
Secondary disk category |
Must match the primary disk in category, performance level, and capacity |
Disk operation limits
The following table lists disk operation limits for async replication and replication pair-consistent groups.
Notes referenced in the table:
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After a replication pair is activated, the secondary disk becomes read-only.
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Due to the RPO, a snapshot of the primary disk may differ from a snapshot taken at the same time on the secondary disk.
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Both disks in a replication pair must be either encrypted or unencrypted. Cross-replication between encrypted and unencrypted disks is not supported.
|
Operation |
Primary disk |
Secondary disk |
|
Read and write |
Read and write |
Read-only (see note 1) |
|
Disk deletion |
Not supported |
Not supported |
|
Disk initialization |
Not supported |
Not supported |
|
Disk resizing |
Not supported |
Not supported |
|
Disk attaching |
Supported |
Not supported |
|
Snapshot creation |
Supported |
Supported (see note 2) |
|
Rollback based on snapshots |
Supported |
Not supported |
|
Disk category change |
Not supported |
Not supported |
|
Performance level change |
Not supported |
Not supported |
|
Disk encryption |
Supported |
Supported (see note 3) |
|
Multi-attach |
Not supported |
Not supported |
|
Disk migration with instances |
Not supported |
Not supported |
Billing
Async replication uses pay-as-you-go billing.
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You are charged based on the total amount of data replicated.
Cost = Data volume unit price × Total replicated data size.
Pay-as-you-go charges apply only to cross-region replication. Cross-zone replication within the same region is free of charge.
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Disks created at the disaster recovery site during disaster recovery drills are billed on a pay-as-you-go basis.
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RTC activation fees:
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If RTC is enabled for a cross-region async replication pair, an additional charge applies based on the amount of replicated data. The unit price is USD 0.0143 per GB.
RTC fees do not apply to cross-zone replication within the same region.
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Terms
Key terms for disk disaster recovery:
|
Term |
Description |
|
Asynchronous replication |
Async replication periodically replicates data from one disk to another across regions or zones. Because replication is not real-time, data on the source and destination disks may differ. |
|
Primary site |
The data center where the primary disk resides. A primary site independently handles business operations. After a reverse replication, the primary site becomes the secondary site. |
|
Secondary site |
The data center where the secondary disk resides. The secondary site serves as a backup for the primary site. If the primary site fails, the secondary site takes over to ensure business continuity. After a reverse replication, the secondary site becomes the primary site. |
|
Primary disk |
The source disk from which data is replicated. After a reverse replication, the primary disk becomes the secondary disk. |
|
Secondary disk |
The destination disk to which data is replicated. After a reverse replication, the secondary disk becomes the primary disk. |
|
RPO |
Recovery point objective. The maximum amount of data loss measured in time. The default RPO for async replication is 15 minutes, meaning data written to the primary disk in the last 15 minutes may be lost during a failure. |
|
RTO |
Recovery time objective. The time required for a primary disk to recover after a failure. For example, an RTO of 1 hour means the disk can resume normal operations within 1 hour. |
|
Async replication relationship |
The replication relationship between a primary disk and a secondary disk, along with the async replication configuration. |
|
Replication pair |
A disk pair with an async replication relationship. A replication pair-consistent group can contain multiple replication pairs. |
|
Failover |
Enables read and write permissions on the secondary disk so it can take over from the failed primary disk. |
|
Reverse replication |
Reverses the replication direction of a replication pair, replicating data from the original secondary disk to the original primary disk. |
Procedures
Choose the procedure that matches your scenario:
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Implement disaster recovery for a single disk set
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Implement disaster recovery for multiple disk sets