What watermarks are

You use watermark settings to globally manage a Storage Node’s usable storage space. Watermark settings trigger alarms that assist you in monitoring available storage and determining when to add Storage Nodes.

A Storage Node becomes read-only when all of a Storage Node’s object stores reach the Storage Volume Hard Read-Only Watermark. If available space falls below this configured watermark amount, a Notice alarm is triggered for the Storage Status (SSTS) attribute. The alarm notifies you to manage storage proactively so that you add capacity only when necessary.

You can view the StorageGRID Webscale system’s current watermark values at any time. Go to Configuration > Storage Options > Overview.


Watermarks

Watermark related attributes


Watermarks diagram

Watermark Name Default Setting Code Description
Storage Volume Hard Read-Only Watermark 5 GB VROM Indicates when a Storage Node transitions to hard read-only mode. Hard read-only mode means that the Storage Node is read-only and no longer accepts write requests.

The Storage Volume Hard Read-Only Watermark value is calculated against the Total Space value for the Storage Node, but measured against the Total Usable Space value for the Storage Node. When the value of Total Usable Space falls below the value of Storage Volume Hard Read-Only Watermark, the Storage Node transitions to hard read-only mode.

The Storage Volume Hard Read-Only Watermark value must be less than value for The Storage Volume Soft Read-Only Watermark.

Storage Volume Soft Read-Only Watermark 10 GB VHWM

Indicates when a Storage Node transitions to soft read-only mode. Soft read-only mode means that the Storage Node advertises read-only services to the rest of the StorageGRID Webscale system, but fulfills all pending write requests.

The Storage Volume Soft Read-Only Watermark value is calculated against the Total Space value for the Storage Node, but measured against the Total Usable Space value for the Storage Node. When the value of Total Usable Space falls below the value of Storage Volume Soft Read-Only Watermark, the Storage Node transitions to soft read-only mode:
  • The Storage State – Current (SSCR) changes to Read-Only. If Storage State – Desired is set to Online, Storage Status (SSTS) changes to Insufficient Free Space and a Notice alarm is triggered.
  • An alarm for Total Usable Space (Percent) (SAVP) can be triggered, depending on the relationship between the watermark setting (in bytes) and the alarm settings (in percent).

The Storage Node is writable again if Total Usable Space (STAS) becomes greater than Storage Volume Soft Read-Only Watermark.

Storage Volume Read-Write Watermark 30 GB VLWM

Indicates when a Storage Node that has transitioned to read-only mode is allowed to become read-write again, specifically when one of the constituent volumes determines that its available space exceeds this setting.

The Storage Volume Read-Write Watermark value must be greater than the value for Storage Volume Soft Read-Only Watermark.

The value for a volume's available space is located on the Support > Grid Topology > storage node > LDR > Storage > Overview page.

Metadata Reserved Space 3 TB CAWM The amount of space reserved on storage volume 0 for metadata storage. Metadata Reserved Space is subdivided into space for object metadata (Metadata Allowed Space, or CEMS) and space for essential database operations, such as compaction and repair.
Note: If the storage capacity of volume 0 is less than 500 GB (non-production use only), 10% of the storage volumeʹs capacity is reserved for metadata.