/opt/pf9/data/instances or /pf9/instances path consuming space above the threshold

Problem

Why /opt/pf9/data/instances or /pf9/instances path consuming space above the threshold on the PMO Host.

Environment

• Platform9 Managed OpenStack - All versions

Cause

• All the VMs that are created from Image & not from a volume i.e., VMs with Ephemeral Storage will consume a lot of space at /opt/pf9/data/instances or /pf9/instances.
• This is because the boot volume of the VMs will reside at /opt/pf9/data/instances or /pf9/instances location.

Resolution

It is recommended to use persistent storage, such as Cinder, when creating instances instead of ephemeral storage. This will prevent issues with the /opt/pf9/data/instances or /pf9/instances path exceeding the space usage threshold. Additionally, there are several advantages to using persistent storage.

Ephemeral Storage

Ephemeral storage in OpenStack is directly attached to the compute instance's lifecycle. It is typically located on the physical disks of the compute node where the instance runs. Here are the key characteristics of ephemeral storage:

• Lifecycle: Ephemeral storage is tightly coupled with the instance. When an instance is terminated, the ephemeral storage is also destroyed.
• Performance: Generally offers faster data access as it is directly attached to the host machine.
• Use Cases: Suitable for temporary storage needs where data persistence is not required beyond the life of an instance.

Cinder (Block Storage)

Cinder, OpenStack’s block storage service, offers persistent storage solutions that are not tied to the lifecycle of individual compute instances. Here are the important features:

• Persistence: Cinder volumes remain intact regardless of the state of an instance. You can detach a volume from one instance and attach it to another without losing data.
• Performance: Generally provides good performance and is suitable for scenarios requiring frequent read/write operations. Performance can be influenced by the network and the underlying storage hardware.
• Flexibility: Volumes can be easily resized, and different types of storage (SSD, HDD, etc.) can be used depending on performance needs.
• Data Security: Since volumes can be retained even after an instance is deleted, backups and snapshots can be managed more effectively.

Additional Information

Refer this KB for Identifying Ephemeral vs Boot-From-Volume Instances.