---
title: "Cluster MD Blocks alerts"
slug: "cluster-md-blocks-alerts"
description: "Monitor MD Block usage and troubleshoot alerts effectively to optimize your system's performance and prevent reaching capacity limits."
updated: 2026-10-27T19:37:32Z
published: 2026-10-28T19:53:12Z
canonical: "docs.vastdata.com/cluster-md-blocks-alerts"
---

> ## Documentation Index
> Fetch the complete documentation index at: https://docs.vastdata.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Cluster MD Blocks alerts

## Overview

This KB covers the relevant information for the following alerts:

1. **Cluster MD Block usage is above 88% /100%** The alerts usually mean the system is approaching its MD Block limits.

## Background

The system contains DBoxes; each DBox has a limit on the number of MD blocks, which depends on the DBox model and the SCMs. In some scenarios, the system can reach the MD block limit before reaching the capacity/handle limits of the system. Some features that can consume many MD blocks are snapshots (especially the snapshot policy for long-term storage) and a vast catalog.

## Monitor

1. For looking into the MD Block usage, it is shown in the main dashboard in the VMS GUI - in this case, the MD Block used space is 66.22%(relevant metric for MD Block usage in Analytics is **MD Usage percent,** this metric is a combination of the MD Block and Token mapper usage)

![Data reduction UI screenshot](https://cdn.us.document360.io/89b91113-5dc6-49db-86ec-57b16dc8ce56/Images/Documentation/253b91ea-f587-4e8f-8dd9-e2b8a47e93c4.png?sv=2026-02-06&spr=https&st=2026-11-08T09%3A29%3A17Z&se=2026-11-08T10%3A29%3A17Z&sr=c&sp=r&sig=3dCs%2BdUvxp%2BIXmKHy86NBA3HaVUk75QpK5udFFHqpw0%3D)

Data reduction UI screenshot

1. For tracking MD usage on the cluster, please create a graph in Analytics called **MD usage** that includes the following metrics: **Capacity,md_total_blocks,** **Capacity,md_used_blocks,** and **Capacity,****md_used_blocks_percent**. In this example, the total MD blocks of the cluster are **1077004800**, the used MD Blocks in the system are **649013413**, MD usage percent is **~60.2%** → **This percent** is according to **the total MD usage of the system** → since 4.7.0-sp18, the MD Block usage limit is normalized to 100% according to the limit of 91%, the calculation for normalizing the MD usage in such case is: (**649013413** /(**1077004800*** 0.91)) * 100 = ~**66.22**%

![MetaData usage graph](https://cdn.us.document360.io/89b91113-5dc6-49db-86ec-57b16dc8ce56/Images/Documentation/92965646-be28-4fac-bc4e-67056ae4424a.png?sv=2026-02-06&spr=https&st=2026-11-08T09%3A29%3A17Z&se=2026-11-08T10%3A29%3A17Z&sr=c&sp=r&sig=3dCs%2BdUvxp%2BIXmKHy86NBA3HaVUk75QpK5udFFHqpw0%3D)

MetaData usage graph

## Troubleshooting

1. A new feature introduced in 5.1 may help reduce the system's MD block usage.
2. If the upgrade to 5.1 is not possible and the VAST Catalog is enabled, our recommendation is to consider disabling the VAST Catalog, since it may consume a lot of MD usage. A new feature was introduced in 5.1 that helps to decrease the MD that is consumed by the VAST Catalog.
3. If the system is already in 5.1 or above, our recommendation is to consider removing or deleting unnecessary data or snapshots.
4. In case deleting data or removing snapshots is not an option, one of the options is to consider expanding the system with additional storage in the cluster.

## Related Articles

- Capacity terms can be found at [VAST Cluster 5.3 Administrator's Guide](/docs-5-5/docs/dashboard#capacity) (requires a valid user to access the Vast customer portal) under the **Capacity** section.