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

# About placement groups

A placement group is a policy that controls whether Virtual Machines share the same physical server or are spread across different ones. Groups are [configured](/cloud/virtual-instances/placement-groups/configure-a-placement-group) and assigned to instances at creation or afterward.

## Types of groups

Three placement group types determine how Virtual Machines are distributed across physical servers.

* Affinity groups assemble Virtual Machines on the same server, so they exchange data faster due to physical proximity.

* Anti-affinity groups place Virtual Machines on separate physical servers. A failure on one server leaves instances on the others unaffected.

* Soft anti-affinity groups encourage separation across servers but allow placement on the same hardware if no separate server is available. This avoids creation failures that a strict anti-affinity policy would trigger under the same conditions.

## FAQ

Placement groups have a few constraints that affect how instances are created and assigned.

**What happens if instances are not added to a placement group?** They are placed on physical servers at random — they could end up all on the same server or spread across different ones.

**How many placement groups can a Virtual Machine belong to at the same time?** Only one. A Virtual Machine cannot be added to two groups simultaneously.