netdata/docs/netdata-agent/sizing-netdata-agents/disk-requirements-and-retention.md

Disk Requirements & Retention

Database Modes and Tiers

Netdata offers two database modes to suit your needs for performance and data persistence:

Mode	Description
dbengine (default)	High-performance, multi-tier storage with compression. Metric samples are cached in memory and then written to disk in multiple tiers for efficient retrieval and long-term storage.
ram	In-memory storage. Metric samples are stored in memory only, and older data is overwritten as new data arrives. This mode prioritizes speed, making it ideal for Netdata Child instances that stream data to a central Netdata parent.

dbengine

Netdata's dbengine mode efficiently stores data on disk using compression. The actual disk space used depends on how well the data compresses. This mode uses a tiered storage approach: data is saved in multiple tiers on disk. Each tier retains data at a different resolution (detail level). Higher tiers store a down-sampled (less detailed) version of the data found in lower tiers.

gantt
    dateFormat  YYYY-MM-DD
    tickInterval 1week
    axisFormat    
    todayMarker off
    tier0, 14d       :a1, 2023-12-24, 7d
    tier1, 60d       :a2, 2023-12-01, 30d
    tier2, 365d      :a3, 2023-11-02, 59d

dbengine supports up to five tiers. By default, three tiers are used:

Tier	Resolution	Uncompressed Sample Size	Usually On Disk
tier0	native resolution (metrics collected per-second as stored per-second)	4 bytes	0.6 bytes
tier1	60 iterations of tier0, so when metrics are collected per-second, this tier is per-minute.	16 bytes	6 bytes
tier2	60 iterations of tier1, so when metrics are collected per second, this tier is per-hour.	16 bytes	18 bytes

Configuring dbengine mode and retention:

• Enable dbengine mode: The dbengine mode is already the default, so no configuration change is necessary. For reference, the dbengine mode can be configured by setting [db].mode to dbengine in netdata.conf.
• Adjust retention (optional): see Change how long Netdata stores metrics.

ram

ram mode can help when Netdata shouldn’t introduce any disk I/O at all. In both of these modes, metric samples exist only in memory, and only while they’re collected.

When Netdata is configured to stream its metrics to a Metrics Observability Centralization Point (a Netdata Parent), metric samples are forwarded in real-time to that Netdata Parent. The ring buffers available in these modes are used to cache the collected samples for some time, in case there are network issues, or the Netdata Parent is restarted for maintenance.

The memory required per sample in these modes, is four bytes: ram mode uses mmap() behind the scene, and can be incremented in steps of 1024 samples (4KiB). Mode ram allows the use of the Linux kernel memory dedupper (Kernel-Same-Page or KSM) to deduplicate Netdata ring buffers and save memory.

Configuring ram mode and retention:

• Enable ram mode: To use in-memory storage, set [db].mode to ram in your netdata.conf file. Remember, this mode won't retain historical data after restarts.
• Adjust retention (optional): While ram mode focuses on real-time data, you can optionally control the number of samples stored in memory. Set [db].retention in netdata.conf to the desired number in seconds. Note: If the value you choose isn't a multiple of 1024, Netdata will automatically round it up to the nearest multiple.