What watermarks are

You use watermark settings to globally manage a Storage Node’s usable storage space. Watermarks settings trigger alarms that assist you in monitoring available storage and determine when adding Storage Nodes is required.

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. This allows you to manage storage proactively and add capacity only when necessary.

The StorageGRID Webscale system’s current watermark values can be obtained at any time. Go to Configuration > Storage Options > Overview.


Watermarks

Watermark related attributes


Watermarks diagram

Attribute Name Default Setting Code Description
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 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.

Metadata Reserved Space Watermark 2 TB CAWM The amount of free space reserved on object store volume 0 for object metadata storage. If the storage capacity of volume 0 is less than 500 GB, only 10% of the storage volumeʹs capacity is reserved for metadata.