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Redis Enterprise is a fully durable database. It supports the following data persistence mechanisms:
Snapshots and backup are designed for two different things. While snapshot supports data durability (i.e. to automatically recover data when there is no copy of the dataset in memory), backup supports disaster recovery (i.e. when the entire cluster needs to be rebuilt from scratch).
In cloud native deployments such as a public cloud, private cloud, or virtual private cloud, ephemeral (instance) storage cannot be used for durability purposes. Instead, a network-attached storage like Amazon Elastic Block Store (EBS), Microsoft Azure Disk Storage, or Google Cloud Platform Persistent Disk is required. That’s because, just as it sounds, ephemeral storage is ephemeral! When a cloud instance fails (which is relatively common), the contents of its local disk are also lost.
The Redis Enterprise cluster is designed to work with network-attached storage for data persistence. By default, every node in the cluster is connected to a network-attached storage resource, making the cluster immune to data-loss events such as multiple node failures with no copies of the dataset left in DRAM. This durability-proven architecture is illustrated here:
As illustrated above, in cases where there is no copy of the dataset left in DRAM, Redis Enterprise will find the most recent copy of the dataset in the network-attached devices that were connected to the failed node, and use that to populate the Redis shard on the new cloud instance.
By default, when data persistence is enabled Redis Enterprise sets data persistence at the slave of each shard of the database. In this configuration there is no impact on performance, as the master shard is not affected by the slowness of the disk; on the other hand, replication adds latencies that may break the data persistence SLA. Therefore, Redis Enterprise allows you to enable data persistence on both the master and slave shards. This is a more reliable configuration that doesn’t infringe on your data persistence SLA, but if the disk speed cannot cope with the throughput of ‘writes,’ it will affect the latency of your database, as Redis delays its processing when it cannot commit to disk. If you use Redis Enterprise DBaaS deployments (Cloud or VPC) you will automatically be tuned to work with a storage engine and the right shards configuration to support your persistent storage load; in an on-premises deployment, we recommend you consult with Redis solutions architects regarding your sizing. Data persistence options are shown here:
Redis Enterprise enhances the Redis storage engine to increase the throughput of the Redis core with data persistence enabled, and to better utilize cluster resources by allowing multiple Redis instances to run on the same cluster node without affecting performance:
A storage engine benchmark performed by Dell-EMC and Redis showed that when using Redis Enterprise’s enhanced storage engine with Dell-EMC VMAX, Redis performance is nearly unaffected by AOF every-write operation, as shown here:
More information on this benchmark can be found here:
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