Secondary storage

This is also known as Hot/Cold storage.

Secondary storage is intended for usages where the primary is “low-latency and fast”, such as NVME, and the secondary is “high-latency but very large”, such as a SAN spanning many spinning disks.

Only segment files get moved to the secondary storage. Older files get moved before younger ones.

Files get moved based on disk space available

When enabled Humio will move segment files to secondary storage once the primary disk reaches the usage threshold set using PRIMARY_STORAGE_PERCENTAGE. Humio does not check what is using the space, it bases the decision on what the OS responds for “disk space used” and “disk space total” for the mount point that the primary data dir is on.

When the threshold is exceeded Humio will copy files totaling the excess number of bytes to the secondary storage, and then delete the segment files from the primary data dir. The files are selected based on the latest event timestamp in them, to keep most recent events on the primary disk. This is done to get the best possible query performance from the assumed faster primary drive, since Humio is normally used for querying the latest data.

The extra storage gained is thus almost the available space on of the secondary data dir, as only a single segment file is ever present on both volumes at once.

Note that the secondary dir needs to be private to the Humio node, just like the primary dir does. Never share data directories across Humio nodes!


A server with 1TB NVME being used for system files, Kafka data and Humio data. Adding a 2TB SAN connection (or 2x2TB local spinning disks in a mirror) and then designating that as secondary storage directory allows Humio to store up to 2.8TB, while still querying the latest ~800GB from the NVME, and also keeping all segment files still being constructed on the NVME. When searching beyond what the NVME holds, Humio will read from the slower disks.


Humio needs to be told where to store the secondary copies i.e. the location of the fileystem on the slower drive.

When using docker, make sure to mount the secondary directory into the container as well.

# SECONDARY_DATA_DIRECTORY enables the feature
# and sets where to store the files.

# PRIMARY_STORAGE_PERCENTAGE options decides the amount of data (Humio
# and otherwise) that the drive holding the data dir must at least hold
# before Humio decides to move any segments files to the secondary location.
# If set to zero, Humio will move files to secondary as soon as possible,
# which is when they become immutable completed segment files.
# (Default 80)