Installation Strategy and Preparation

Before embarking on the installation process for Trilio in your OpenStack environment, it is highly advisable to carefully consider several key elements. These considerations will not only streamline the installation procedure but also ensure the optimal setup and functionality of Trilio's solutions within your OpenStack infrastructure.

Tenant Quotas

Trilio leverages Cinder snapshots to facilitate the computation of both full and incremental backups.

When executing full backups, Trilio orchestrates the generation of Cinder snapshots for all volumes included in the backup job. These Cinder snapshots remain intact for subsequent incremental backup image calculations.

During incremental backup operations, Trilio generates fresh Cinder snapshots and computes the altered blocks between these new snapshots and the earlier retained snapshots from full or previous backups. The old snapshots are subsequently deleted, while the newly generated snapshots are preserved.

Consequently, it becomes imperative for each tenant benefiting from Trilio's backup functionality to possess adequate Cinder snapshot quotas capable of accommodating these supplementary snapshots. As a guiding principle, it is recommended to append 2 snapshots for each volume incorporated into the backup quotas for the respective tenant. Additionally, a commensurate increase in volume quotas for the tenant is advisable, as Trilio briefly materializes a volume from the snapshot to access data for backup purposes.

During the restoration process, Trilio generates supplementary instances and Cinder volumes. To facilitate seamless restore operations, tenants should maintain adequate quota levels for Nova instances and Cinder volumes. Failure to meet these quota requirements may lead to disruptions in restoration procedures.

AWS S3 Eventual Consistency

The AWS S3 object consistency model includes:

  1. Read-after-write

  2. Read-after-update

  3. Read-after-delete

Each of these models explains how an object becomes consistent after being created, updated, or deleted. None of these methods ensures strong consistency, leading to a delay before an object becomes fully consistent.

Although Trilio has introduced measures to address AWS S3's eventual consistency limitations, the exact time an object achieves consistency cannot be predicted through deterministic means.

There is no official statement from AWS on how long it takes for an object to reach a consistent state. However, read-after-write has a shorter time to reach consistency compared to other IO patterns. Therefore, our solution is designed to maximize the read-after-write IO pattern.

AWS Region Considerations

The time in which an object reaches eventual consistency also depends on the AWS region.

For instance, the AWS-standard region doesn't offer the same level of strong consistency as regions like us-east or us-west. Opting for these regions when setting up S3 buckets for Trilio is advisable. While fully avoiding the read-after-update IO pattern is complex, we've introduced significant access delays for objects to achieve consistency over longer periods. On rare occasions when this does happen, it will cause a backup failure and require a retry.

Trilio Cluster

Trilio can be deployed as a single node or a three-node cluster. It is highly recommended that Trilio is deployed as a three-node cluster for fault tolerance and load balancing. Starting with the 3.0 release, Trilio requires additional IP or FQDN for the cluster and is required for both single-node and three-node deployments. Cluster IP a.k.a virtual IP is used for managing clusters and is used to register the Trilio service endpoint in the keystone service catalog.

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