Redis on Flash
Redis on Flash (RoF) offers Redis Enterprise users the unique ability to have large Redis databases but at significant cost savings. Where standard Redis databases must all be in RAM, Redis on Flash enables your databases to span both RAM and dedicated flash memory in the form of SSDs (solid state drives).
Your data is distributed between RAM and flash memory so that your frequently used data is accessible in RAM, while the values you need less often are stored on the flash memory. Since flash memory usually comes with more storage space and less cost than RAM, this can result in significant savings for large datasets.
Just like all-RAM databases, RoF is compatible with existing Redis applications. Databases that employ RoF are identical to all-RAM Redis Enterprise Software databases in characteristics and features.
Redis on Flash is also supported on Redis Cloud and Redis Enterprise Software for Kubernetes.
Use cases
The benefits associated with Redis on Flash are dependent on the use case.
Redis on Flash is ideal when your:
- working set is significantly smaller than your dataset
- average key size is smaller than average value size
- most recent data is the most frequently used
Redis on Flash is not recommended for:
- Long key names (all key names are stored in RAM)
- Broad access patterns (any value could be pulled into RAM)
- Large working sets (working set is stored in RAM)
- Frequently moved data (moving to and from RAM too often can impact performance)
Redis on Flash is not intended to be used for persistent storage. Redis Enterprise Software database persistent and ephemeral storage should be on different disks, either local or attached.
Where is my data?
When using Redis on Flash, RAM storage holds:
- All keys (names)
- Key indexes
- Dictionaries
- Hot data (working set)
All data is accessed through RAM. If a value in flash memory is accessed, it becomes part of the working set and is moved to RAM. These values are referred to as “hot data”.
Inactive or infrequently accessed data is referred to as “warm data” and stored in flash memory. When more space is needed in RAM, warm data is moved from RAM to flash storage.
RAM to Flash ratio
You can easily configure or tune the ratio of RAM-to-Flash for each database independently, optimizing performance for your specific use case. This is an online operation requiring no downtime for your database.
The RAM size cannot be smaller than 10% or larger than 60% of the total memory. We recommend you keep at least 20% of all values in RAM.
Flash memory
Implementing Redis on Flash requires preplanning around memory and sizing. Considerations and requirements for Redis on Flash include:
- Flash memory must be locally attached (as opposed to network attached.
- Flash memory must be dedicated to RoF and not shared with other parts of the database, such as durability, binaries, or persistence.
- For the best performance, the SSDs should be NVMe based, but SATA can also be used.
Once these requirements are met, you can create and manage both Redis on Flash databases and all-RAM databases in the same cluster.
When you begin planning the deployment of Redis on Flash in production, we recommend working closely with the Redis technical team for sizing and performance tuning.
Cloud environments
When running in a cloud environment:
- Flash memory is on the ephemeral SSDs of the cloud instance.
- Persistent database storage needs to be network attached (for example, AWS EBS for AWS).
On-premises environments
When you begin planning the deployment of Redis on Flash in production, we recommend working closely with the Redis technical team for sizing and performance tuning.
On-premises environments support more deployment options than other environments such as:
- Using Active-Active distributed databases
- Using supported modules