Chapter 9. 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.

9.1. Available persistent storage options

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

Table 9.1. Available storage options

Storage typeDescriptionExamples

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 [1], and Vendor NFS

Object

  • Accessible through a REST API endpoint
  • Configurable for use in the OpenShift image registry
  • Applications must build their drivers into the application and/or container.

AWS S3

  1. NetApp NFS supports dynamic PV provisioning when using the Trident plugin.
Important

Currently, CNS is not supported in OpenShift Container Platform 4.10.

9.3. Data storage management

The following table summarizes the main directories that OpenShift Container Platform components write data to.

Table 9.3. Main directories for storing OpenShift Container Platform data

DirectoryNotesSizingExpected growth

/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.

/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.

9.4. Optimizing storage performance for Microsoft Azure

OpenShift Container Platform and Kubernetes are sensitive to disk performance, and faster storage is recommended, particularly for etcd on the control plane nodes.

For production Azure clusters and clusters with intensive workloads, the virtual machine operating system disk for control plane machines should be able to sustain a tested and recommended minimum throughput of 5000 IOPS / 200MBps. This throughput can be provided by having a minimum of 1 TiB Premium SSD (P30). In Azure and Azure Stack Hub, disk performance is directly dependent on SSD disk sizes. To achieve the throughput supported by a Standard_D8s_v3 virtual machine, or other similar machine types, and the target of 5000 IOPS, at least a P30 disk is required.

Host caching must be set to ReadOnly for low latency and high IOPS and throughput when reading data. Reading data from the cache, which is present either in the VM memory or in the local SSD disk, is much faster than reading from the disk, which is in the blob storage.