Optimizing storage

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 OKD 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 OKD.
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 ^[1], and Vendor NFS
Object	Accessible through a REST API endpoint Configurable for use in the OKD Registry Applications must build their drivers into the application and/or container.	AWS S3

NetApp NFS supports dynamic PV provisioning when using the Trident plug-in.

Currently, CNS is not supported in OKD 4.6.

Recommended configurable storage technology

The following table summarizes the recommended and configurable storage technologies for the given OKD cluster application.

Table 2. Recommended and configurable storage technology
Storage type	ROX¹	RWX²	Registry	Scaled registry	Metrics³	Logging	Apps
Block	Yes⁴	No	Configurable	Not configurable	Recommended	Recommended	Recommended
File	Yes⁴	Yes	Configurable	Configurable	Configurable⁵	Configurable⁶	Recommended
Object	Yes	Yes	Recommended	Recommended	Not configurable	Not configurable	Not configurable⁷
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 persistent volume claims (PVCs) 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 OKD’s PVs or PVCs. Apps must integrate with the object storage REST API.

A scaled registry is an OKD registry where two or more pod replicas are running.

Specific application storage recommendations

Testing shows issues with using the NFS server on Fedora as storage backend for core services. This includes the OpenShift Container Registry and Quay, Prometheus for monitoring storage, and Elasticsearch for logging storage. Therefore, using Fedora 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 OKD core components.

Registry

In a non-scaled/high-availability (HA) OKD registry cluster deployment:

The storage technology does not have to support RWX access mode.
The storage technology must ensure read-after-write consistency.
The preferred storage technology is object storage followed by block storage.
File storage is not recommended for OKD registry cluster deployment with production workloads.

Scaled registry

In a scaled/HA OKD registry cluster deployment:

The storage technology must support RWX access mode.
The storage technology must ensure read-after-write consistency.
The preferred storage technology is object storage.
Amazon Simple Storage Service (Amazon S3), Google Cloud Storage (GCS), Microsoft Azure Blob Storage, and OpenStack Swift are supported.
Object storage should be S3 or Swift compliant.
For non-cloud platforms, such as vSphere and bare metal installations, the only configurable technology is file storage.
Block storage is not configurable.

Metrics

In an OKD hosted metrics cluster deployment:

The preferred storage technology is block storage.
Object storage is not configurable.

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

Logging

In an OKD hosted logging cluster deployment:

The preferred storage technology is block storage.
Object storage is not configurable.

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

OKD 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.

Data storage management

The following table summarizes the main directories that OKD components write data to.

Table 3. Main directories for storing OKD data
Directory	Notes	Sizing	Expected growth
*/var/lib/etcd*	Used for etcd storage when storing the database.	Less than 20 GB. Database can grow up to 8 GB.	Will grow slowly with the environment. Only storing metadata. Additional 20-25 GB for every additional 8 GB of memory.
*/var/lib/containers*	This is the mount point for the CRI-O runtime. Storage used for active container runtimes, including pods, and storage of local images. Not used for registry storage.	50 GB for a node with 16 GB memory. Note that this sizing should not be used to determine minimum cluster requirements. Additional 20-25 GB for every additional 8 GB of memory.	Growth is limited by capacity for running containers.
*/var/lib/kubelet*	Ephemeral volume storage for pods. This includes anything external that is mounted into a container at runtime. Includes environment variables, kube secrets, and data volumes not backed by persistent volumes.	Varies	Minimal if pods requiring storage are using persistent volumes. If using ephemeral storage, this can grow quickly.
*/var/log*	Log files for all components.	10 to 30 GB.	Log files can grow quickly; size can be managed by growing disks or by using log rotate.