# Data Persistence

In-Memory DB supports various persistence options. For more information, refer to the [<mark style="color:blue;">In-Memory DB documentation</mark>](https://redis.io/docs/latest/operate/oss_and_stack/management/persistence/).

IONOS Cloud DBaaS completely supports a requirements-based persistence mechanism for In-Memory DB. You can either choose to use In-Memory DB (RDB) and Append-Only File (AOF) data persistence options or combine both for durable storage. Contextually, data persistence refers to the information saved on a reliable non-volatile storage medium (for example, memory, HDD, or SSD) that can be recovered even during a system failure. Hence, persistent data—or non-volatile storage—can save data that is still accessible even during a crash.

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**Note:** To ensure the safety of your data during failures or maintenance, we strongly recommend using either RDB and AOF or one of the following persistence mechanisms so that In-Memory DB transfers the whole dataset to the disk.
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## RDB

An RDB is a compact single file called a snapshot, representing your In-Memory DB data in a binary format. Due to its compactness, storage of In-Memory DB data is quicker, and retrieval is swifter. IONOS Cloud DBaaS periodically writes In-Memory DB in-memory data to disk files with the .rdb file extensions, thus creating multiple snapshot files for each write operation. In-Memory DB writes the entire point-in-time view of the dataset to the persistent storage.

The default RDB settings for snapshots are as follows:

* every one hour for a single change or write operation.
* every five minutes for at least 100 write operations.
* every minute for at least 10000 write operations.

DBaaS clears In-Memory DB in-memory data soon after creating a snapshot on the disk. Because it is automated and periodic, the write operation will lessen your workload and resume activities quickly in case of a failure. During a system crash, you can select from multiple snapshot files stack and restore the appropriate version. You can also back it up to a [<mark style="color:blue;">S3 bucket</mark>](https://docs.ionos.com/sections-test/guides/storage-and-backup/ionos-object-storage/get-started/create-bucket).

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**Note:** The disadvantage of this method is that you may lose data in the event of a failure because snapshots are saved at regular intervals.
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## AOF

In-Memory DB provides another data persistence option called the AOF, which logs all its data into a log file. Every time In-Memory DB performs a write operation, it appends it to the AOF file. The AOF file is saved with a .aof extension and can be used to recover the entire replicaset in case of a crash. You can use the file to reconstruct the original dataset during a server restart.

In-Memory DB automatically rewrites an AOF file in the background when it reaches its maximum capacity, compacting it to save just the most recent data version.

## Benefits of RDB and AOF combination

* Regular backups of the In-Memory DB dataset.
* Secondary instances can use the RDB and AOF files to rebuild the dataset from the primary instance during replication.
* The restart time is faster than recreating the dataset from scratch, thus enhancing the performance, scalability, and reliability.

## Determine Provisioned Block Storage in an In-Memory DB Cluster

The provisioned Block Storage in an In-Memory DB cluster depends on the amount of RAM configured and the data persistence mode selected.

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**Note:** A minimum storage of 10 GB is applied for all data persistence modes in each node.
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The amount of provisioned Block Storage is based on the relationship below:

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**Note:**

* The RAM specified in the relationship table below refers to the Dedicated Core RAM.
* The total RAM is also determined by the number of nodes in your In-Memory DB cluster.
  {% endhint %}

| Data Persistence | Storage |
| ---------------- | ------- |
| None             | 1 x RAM |
| RDB              | 2 x RAM |
| AOF              | 4 x RAM |
| RDB & AOF        | 8 x RAM |