What Metadata Reserved Space is

StorageGRID maintains three copies of object metadata at each site to provide redundancy and to protect object metadata from loss. The three copies are evenly distributed across all Storage Nodes at each site using the space reserved for metadata on storage volume 0 of each Storage Node.

The Metadata Reserved Space (CAWM) is a system-wide setting that represents the default amount of space reserved for metadata on volume 0 of all Storage Nodes.


CAWM Setting

To view the current setting for Metadata Reserved Space (CAWM), select Configuration > Storage Options > Overview.


Metadata Reserved Space

The Storage Watermarks table on the Storage Options Overview page shows the Metadata Reserved Space (CAWM) setting for all Storage Nodes. However, the actual amount of space reserved for metadata on a specific larger-capacity or non-production Storage Node might be different than the value shown.

A node's actual metadata reserved space depends on the amount of RAM on the Storage Node and the size of volume 0, as follows:

Metadata Allowed Space

Each node's metadata reserved space is subdivided into the space available for object metadata (the Metadata Allowed Space) and the space required for essential database operations, such as compaction and repair. The Metadata Allowed Space value is based on the Metadata Reserved Space (CAWM) setting, and it governs overall object capacity.


Metadata Allowed Space Volume 0
Note: StorageGRID uses the following Prometheus metric (used for the alert system) and an equivalent attribute (used in the legacy alarm system) to represent the Metadata Allowed Space.
  • Prometheus expression: storagegrid_storage_utilization_metadata_allowed_bytes
  • Equivalent attribute: Metadata Allowed Space (CEMS)

For a given Storage Node, the Metadata Allowed Space is controlled by the size of storage volume 0, the amount of RAM on the node, and the actual space reserved for metadata on the node.

To view the space allowed for metadata for a particular Storage Node, do either of the following:
  • Select Node > Storage Node > Storage. Then, hover your cursor over the Storage Used - Object Metadata chart. The Total (allowed) value is 6.44 GB in this example of a Storage Node in a non-production grid.
    Nodes Page Storage Used Object Metadata Allowed
  • Select Support. Then, in the Tools section of the menu, select Grid Topology. Then, select Storage Node > DDS > Data Store. The Metadata Allowed Space is also 6.44 GB in this example of a Storage Node in a non-production grid.
    Grid Topology Metadata Allowed Space

See the monitoring and troubleshooting instructions for more information about the object metadata capacity for each Storage Node.

Summary

For larger Storage Nodes, StorageGRID automatically increases the metadata space reservation to optimize database operations and to increase the grid’s object capacity. The following table summarizes how StorageGRID determines the size of the metadata reserved space and the Metadata Allowed Space for a specific Storage Node:
Size of volume 0 Amount of RAM Metadata Reserved Space (CAWM) setting Actual space reserved for metadata Metadata Allowed Space
<500 GB not applicable not applicable 10% of volume 0 6% of volume 0
>500 GB <128 GB 3 TB (default) 3 TB 1.32 TB
>500 GB >128 GB 3 TB (default) 4 TB 1.98 TB
>500 GB not applicable <4 TB (non-default) CAWM or the size of volume 0, whichever is smaller 60% of the space reserved for metadata, up to 1.32 TB
>500 GB >128 GB >4 TB (non-default) CAWM or the size of volume 0, whichever is smaller 60% of the space reserved for metadata, up to 1.98 TB