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Optimizing storage

Optimizing storage helps to minimize storage use across all resources. By optimizing storage, administrators help ensure that existing storage resources are working in an efficient manner.

Available persistent storage options

Understand your persistent storage options so that you can optimize your OpenShift Container Platform environment.

Table 1. Available storage options
Storage type Description Examples

Block

  • Presented to the operating system (OS) as a block device

  • Suitable for applications that need full control of storage and operate at a low level on files bypassing the file system

  • Also referred to as a Storage Area Network (SAN)

  • Non-shareable, which means that only one client at a time can mount an endpoint of this type

AWS EBS and VMware vSphere support dynamic persistent volume (PV) provisioning natively in OpenShift Container Platform.

File

  • Presented to the OS as a file system export to be mounted

  • Also referred to as Network Attached Storage (NAS)

  • Concurrency, latency, file locking mechanisms, and other capabilities vary widely between protocols, implementations, vendors, and scales.

RHEL NFS, NetApp NFS footnoteref:netappnfs[NetApp NFS supports dynamic PV provisioning when using the Trident plug-in.], and Vendor NFS

Object

  • Accessible through a REST API endpoint

  • Configurable for use in the OpenShift Container Platform Registry

  • Applications must build their drivers into the application and/or container.

AWS S3

Currently, CNS is not supported in OpenShift Container Platform 4.2.

The following table summarizes the recommended and configurable storage technologies for the given OpenShift Container Platform cluster application.

Table 2. Recommended and configurable storage technology
Storage type ROX [1] RWX [2] Registry Scaled registry Metrics [3] Logging Apps

Block

Yes [4]

No

Configurable

Not configurable

Recommended

Recommended

Recommended

File

Yes [4]

Yes

Configurable

Configurable

Configurable [5]

Configurable [6]

Recommended

Object

Yes

Yes

Recommended

Recommended

Not configurable

Not configurable

Not configurable [7]

A scaled registry is an OpenShift Container Platform registry where three or more pod replicas are running.

Specific application storage recommendations

Testing shows issues with using the NFS server on RHEL as storage backend for the container image registry. This includes the OpenShift Container Registry and Quay, Prometheus for monitoring storage, and Elasticsearch for logging storage. Therefore, using NFS to back PVs used by core services is not recommended.

Other NFS implementations on the marketplace might not have these issues. Contact the individual NFS implementation vendor for more information on any testing that was possibly completed against these OpenShift core components.

Registry

In a non-scaled/high-availability (HA) OpenShift Container Platform registry cluster deployment:

  • The preferred storage technology is object storage followed by block storage. The storage technology does not have to support RWX access mode.

  • The storage technology must ensure read-after-write consistency. All NAS storage are not recommended for OpenShift Container Platform Registry cluster deployment with production workloads.

  • While hostPath volumes are configurable for a non-scaled/HA OpenShift Container Platform Registry, they are not recommended for cluster deployment.

Scaled registry

In a scaled/HA OpenShift Container Platform registry cluster deployment:

  • The preferred storage technology is object storage. The storage technology must support RWX access mode and must ensure read-after-write consistency.

  • File storage and block storage are not recommended for a scaled/HA OpenShift Container Platform registry cluster deployment with production workloads.

  • All NAS storage are not recommended for OpenShift Container Platform Registry cluster deployment with production workloads.

Metrics

In an OpenShift Container Platform hosted metrics cluster deployment:

  • The preferred storage technology is block storage.

Testing shows significant unrecoverable corruptions using file storage and, therefore, file storage is not recommended for use with metrics.

There are file storage implementations in the marketplace that might not have these issues. Contact the individual storage vendor for more information on any testing that was possibly completed against these OpenShift core components.

Logging

In an OpenShift Container Platform hosted logging cluster deployment:

  • The preferred storage technology is block storage.

  • It is not recommended to use NAS storage for a hosted metrics cluster deployment with production workloads.

Testing shows issues with using the NFS server on RHEL as storage backend for the container image registry. This includes Elasticsearch for logging storage. Therefore, using NFS to back PVs used by core services is not recommended.

Other NFS implementations on the marketplace might not have these issues. Contact the individual NFS implementation vendor for more information on any testing that was possibly completed against these OpenShift core components.

Applications

Application use cases vary from application to application, as described in the following examples:

  • Storage technologies that support dynamic PV provisioning have low mount time latencies, and are not tied to nodes to support a healthy cluster.

  • Application developers are responsible for knowing and understanding the storage requirements for their application, and how it works with the provided storage to ensure that issues do not occur when an application scales or interacts with the storage layer.

Other specific application storage recommendations

  • OpenShift Container Platform Internal etcd: For the best etcd reliability, the lowest consistent latency storage technology is preferable.

  • It is highly recommended that you use etcd with storage that handles serial writes (fsync) quickly, such as NVMe or SSD. Ceph, NFS, and spinning disks are not recommended.

  • Red Hat OpenStack Platform (RHOSP) Cinder: RHOSP Cinder tends to be adept in ROX access mode use cases.

  • Databases: Databases (RDBMSs, NoSQL DBs, etc.) tend to perform best with dedicated block storage.

1. ReadOnlyMany
2. ReadWriteMany
3. Prometheus is the underlying technology used for metrics.
4. This does not apply to physical disk, VM physical disk, VMDK, loopback over NFS, AWS EBS, and Azure Disk.
5. For metrics, using file storage with the ReadWriteMany (RWX) access mode is unreliable. If you use file storage, do not configure the RWX access mode on any PersistentVolumeClaims that are configured for use with metrics.
6. For logging, using any shared storage would be an anti-pattern. One volume per elasticsearch is required.
7. Object storage is not consumed through OpenShift Container Platform’s PVs/persistent volume claims (PVCs). Apps must integrate with the object storage REST API.