You can monitor the capacity of the vSAN datastore, analyze usage, and view the capacity breakdown at the cluster level.

The cluster Summary page includes a summary of vSAN capacity. You also can view more detailed information in the Capacity monitor.

The capacity screen displays the vSAN capacity usage, capacity history, capacity overview, what if analysis, oversubscription, and usage breakdown.


  1. Navigate to the vSAN cluster.
  2. Click the Monitor tab.
  3. Under vSAN, click Capacity to view the vSAN capacity information.


  • The Capacity Overview displays the storage capacity of the vSAN datastore, including total space, used space, free space, and the space that is actually written and physically consumed on the vSAN disks. For clusters that have the deduplication and compression enabled, you can view the deduplication and compression savings and the deduplication and compression ratio.
    Terms Description
    Total space Total physical space in the cluster.
    Free space Total free space in the cluster.
    Used space Total written physical space in the cluster.
    Actually written Actually used capacity. This capacity is displayed when deduplication or compression are not enabled.
    Object reserved Includes the reservation for objects created with a policy that has specified object space reservation. This capacity is not actually used by the objects.
    Reserved capacity Includes the operations reserve and the host rebuild reserve.
  • What if analysis enables you to estimate the free space while keeping the deduplication ratio as 1. The effective free space is an estimation of free space available based on the storage policy that you selected. The effective free space is smaller than the free space available on the disks either due to the topology or the presence of fault domain in the cluster.

    Oversubscription reports the vSAN capacity required if all the thin provisioned VMs and user objects are used at full capacity. It shows a ratio of the required usage compared with the total vSAN capacity. While calculating the oversubscription, vSAN includes all the available VMs, user objects, and the storage policy overhead and does not consider the vSAN namespace and swap objects.

    Note: Oversubscription is applicable only for vSAN hosts that are running 6.7 Update 1 or later.
  • The Usage breakdown before dedup and compression displays the usage breakdown based on the categories such as VM usage, user objects, and system usage. You can view a pie chart representation of the different usage categories. Click the pie chart to view the details of the selected category.

    Following are the different usage categories available:

    Category Description
    VM usage Displays the following:
    • VM home objects - Usage of VM namespace object.
    • Swap objects - Usage of VM swap files.
    • VMDK - Capacity consumed by VMDK objects that reside on the vSAN datastore that can be categorized as primary data and replica usage. Primary data includes the actual user data written into the physical disk which does not include any overhead. Replica usage displays the RAID overhead for the virtual disk.
    • VM memory snapshots - Usage of memory snapshot file for VMs.
    • Block container volumes (attached to a VM) - Capacity consumed by the container objects that are attached to a VM.
    • vSphere replication persistent state file - vSAN object used to store the persistent state file (PSF) at source site.
    User objects Displays iSCSI objects, block container volumes that are not attached to VM, user-created files, ISO files, VM templates, files shares, file container volumes, and vSAN objects used by the vSphere replication service at the target site.
    System usage Displays the following:
    • Performance management objects - Capacity consumed by objects created for storing performance metrics when you enable the performance service.
    • File system overhead - vSAN on-disk format overhead that may take up on the capacity drives.
    • Checksum overhead - Overhead to store all the checksums.
    • Dedup & compression overhead - Overhead to get the benefits of deduplication and compression. This data is visible only if you enable deduplication and compression.
    • Operations usage - Temporary space usage in a cluster. The temporary space usage includes temporary capacity used for rebalance operations or moving objects due to FTT changes.

When you enable deduplication and compression, it might take several minutes for capacity updates to be reflected in the Capacity monitor, as disk space is reclaimed and reallocated. For more information about deduplication and compression, see "Using Deduplication and Compression" in Administering VMware vSAN.

You can check the history of capacity usage in the vSAN datastore. Click Capacity History, select a time range, and click Show Results.

The Capacity monitor displays two thresholds represented as vertical markers in the bar chart:
  • Operations threshold - Displays the space vSAN requires to perform internal operations in the cluster. If the used space reaches beyond that threshold, vSAN might not be able to operate properly.
  • Host rebuild threshold - Displays the space vSAN requires to tolerate one host failure. If the used space reaches beyond the host rebuild threshold and the host fails, vSAN might not successfully restore all data from the failed host.
If you enable reserved capacity, the Capacity monitor displays the following:
  • Operations reserve - Reserved space in the cluster for internal operations.
  • Host rebuild reserve - Reserved space for vSAN to be able to repair in case of single host failure. The Capacity monitor displays the host rebuild threshold only when the host rebuild reserve is enabled.

If the resynchronization of objects is in progress in a cluster, vSAN displays the capacity used in the capacity chart as operations usage. In case there is enough free space in the cluster, vSAN might use more space than the operations threshold for the resyncing operations to complete faster.

Use Configure to enable the capacity reserve. You can also use Configure > vSAN > Services to enable the capacity reserve. For more information on configuring the reserved capacity, see Configure Reserved Capacity.

In a cluster, if there is more utilization than the host rebuild threshold and the reserved capacity is not enabled, the capacity chart turns yellow displaying a warning state. A health alarm is generated indicating that if the most consumed host fails, vSAN cannot recover the data. If you enable the host rebuild reserve, the capacity chart turns yellow at 80% of the host rebuild threshold. If the used space reaches beyond the operations threshold and the reserved capacity is not enabled, vSAN cannot perform or complete operations such as rebalance, resync object components due to policy changes, and so on. In that case, the bar chart turns red. A health alarm is generated indicating that the disk usage exceeds the operations threshold. For more information about capacity reserve, see About Reserved Capacity.