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LogScale Self-Hosted Deployment
This is an archived version of the documentation downloaded from LogScale Documentation Archives. Up to date documentation, and documentation for later versions, is available on LogScale Documentation

## Secondary Storage

Secondary (warm) storage provides a low-cost means to extend primary storage. As primary storage is typically based on fast but expensive NVMe technology, secondary storage can be used to extend local storage capacity using lower cost SSDs or spinning disks. Because of the use of lower cost technology, secondary storage is often much higher capacity than primary storage. Only segment files get moved to the secondary storage. Older files get moved before more recent ones.

### Files moved based on available disk space

When secondary storage is configured using the `SECONDARY_DATA_DIRECTORY` option, LogScale moves segment files to secondary storage once the primary disk reaches the usage threshold set using `PRIMARY_STORAGE_PERCENTAGE`. LogScale does not check what is using the space; it bases the decision on the OS response to system calls for "disk space used" and "disk space total", for the mount point that the primary data directory is on.

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

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

The secondary directory needs to be private to the LogScale node, just like the primary directory does.

### Note

Never share data directories across LogScale nodes.

As an example, suppose you have a server with 1 TB NVMe being used for system files, and LogScale data. Adding a 2 TB SAN connection (or 2x2 TB local spinning disks in a mirror) and then designating that as secondary storage directory enables LogScale to store up to 2.8 TB, while still querying the latest ~800 GB from the NVMe, and also keeping all segment files still being constructed on the NVMe. When searching beyond what the NVMe holds, LogScale reads from the slower disks.

### Configuration

Secondary storage is configured using the `SECONDARY_DATA_DIRECTORY` variable, as shown in the following example:

ini

    # SECONDARY_DATA_DIRECTORY enables the feature
    # and sets where to store the files.
    SECONDARY_DATA_DIRECTORY=/secondaryMountPoint/humio-data2

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

### Note

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

#### Add a new primary and make the current primary disk secondary

If you have a relatively slow disk as your primary storage, you might want to add a new, faster disk to the server, and use that disk as the primary storage, while leaving the bulk of the data on the old slow disk.

While this is possible, there is a process involved, as only completed segment files can reside in the secondary storage. All other support files, and segment files in progress (mini-segments), need to reside on the primary disk. LogScale must be shut down while this operation takes place.

Only files matching `humiodata.*` (and `bloom5*`) can stay on the secondary storage; everything else must be on the primary. You must move the soft links `*/humiodata.current` along with the files they point to.

You will need to move some specific files from the "new secondary" (old primary) onto the "new primary" while the system is shut down for that to work, as some files must be on the primary. The list below shows their names as they appear in `/humio-data`. The directory structure must be preserved. The files to move are:

- Files matching `dataspace_*/datasource_*/humiodata.current`

- For all the above `humiodata.current` soft links, the file the soft link points to as well.

- `uploadedfiles` directory

- `cluster_membership.uuid` file

- `global-data-snapshot.json` file

If the above files are moved from the secondary to the primary, you may leave the remaining segment files, and start out with almost all data being on secondary. Or, if you want, move selected parts of the completed segment files from secondary to primary as well to get improved performance from the new disk on searches that hit those. For example, you could move all segments that are less than seven days old if that matches the search typical search range for the system.

LogScale does not move files from secondary back to primary. Once the primary is full, LogScale starts migrating segment files from primary to secondary.

### Migrating storage directories

When expanding the capacity for primary or secondary storage, and online expansion is not an option, you can move the existing data stored on the partitions and minimize downtime using rsync. Rsync allows you to sync only the new data between directories.

Assuming you are moving secondary data storage from `/var/lib/humio-secondary` to `/var/lib/humio-secondary-new` you can do an initial rsync while LogScale is running. Make sure your new mount has its owner and user set appropriately, generally `humio:humio`.

shell

    rsync -acv /var/lib/humio-secondary/ /var/lib/humio-new-secondary/

This can be run multiple times.

When you are ready to complete the move, start by stopping LogScale:

shell

    systemctl stop humio

This command may differ depending on your LogScale deployment. To move the data written since your last rsync, the delete option removes files that are no longer needed from the destination. Double check your source and destination directories.

shell

    rsync -acv --delete /var/lib/humio-secondary/ /var/lib/humio-new-secondary/

There are two options for having LogScale use the new partition: you can either update the LogScale configuration to use the new mount or you can remount the new partition in the place of the old partitions mount point.

To update the LogScale configuration appropriately, change either the value of the `DIRECTORY` or `SECONDARY_DATA_DIRECTORY` option in `/etc/humio/server_XX.conf` file to point to the new mount. Then restart LogScale:

shell

    systemctl start humio

To unmount and mount the new partition in place of LogScale, first make sure that the appropriate changes are made for your OS, such as updating the `/etc/fstab`, and mount the new partition in the location of the old one. Once that's done, start LogScale.

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