You must monitor the metadata usage for each Storage Node to ensure that adequate space remains available for essential database operations. If the CDLP alarm and the Low metadata storage alert are triggered, you must add new Storage Nodes.
StorageGRID maintains three copies of object metadata at each site to provide redundancy and to protect object metadata from loss. The three copies are load balanced across all Storage Nodes at each site using space reserved on storage volume 0 of each Storage Node.
The total space reserved on each Storage Node for metadata is known as the Metadata Reserved Space (CAWM). The Metadata Reserved Space is subdivided into the space available for object metadata (the Metadata Allowed Space, or CEMS) and the space required for essential database operations, such as compaction and repair.
If the space used by object metadata is more than 100% of the Metadata Allowed Space, database operations cannot run efficiently and errors will occur.
The Metadata Used Space (Percent) attribute, or CDLP, measures how full the Metadata Allowed Space is. When the Metadata Used Space (Percent) reaches the following thresholds, the CDLP alarm and the Low metadata storage alert are triggered:
When you add the new nodes, the system automatically rebalances object metadata across all Storage Nodes, and the CDLP alarm and the Low metadata storage alert are cleared.
In the following example, object metadata is using more than 100% of the Metadata Allowed Space. This is a critical situation, which will result in inefficient database operation and errors.