You can mount disk volumes to Container Service for Kubernetes (ACK) clusters. This topic describes the features, disk specifications, use scenarios, usage notes, billing rules, and StorageClasses that are related to disk volumes.

Features

Alibaba Cloud disks are block-level storage resources for Elastic Compute Service (ECS). Alibaba Cloud disks provide low latency, high performance, high durability, and high reliability. Alibaba Cloud disks use a distributed triplicate mechanism to ensure data reliability for ECS instances. If service disruptions occur within a zone due to hardware faults, data in that zone is automatically copied to an unaffected disk in another zone to ensure data availability.

Disks are classified into the following categories based on their performance:
  • Enhanced SSDs (ESSDs): ESSDs are based on the next-generation distributed block storage architecture and utilize the 25 Gigabit Ethernet and remote direct memory access (RDMA) technologies. Each ESSD has low latency and can deliver up to 1,000,000 random read/write IOPS. For more information, see ESSDs.

    We recommend that you use ESSDs for scenarios such as online transactional processing (OLTP) databases, NoSQL databases, and Elasticsearch, Logstash, and Kibana (ELK) distributed logs.

  • Standard SSDs: Standard SSDs are high-performance disks that provide consistent high random IOPS and high data reliability.

    We recommend that you use standard SSDs for scenarios such as I/O-intensive applications, small and medium-sized relational databases, and NoSQL databases.

  • Ultra disks: Ultra disks are cost-effective and provide medium random IOPS and high data reliability.

    We recommend that you use ultra disks as system disks or for scenarios such as development and testing.

  • Basic disks: Basic disks are the previous generation of disks and are unavailable for purchase.

Disk specifications

For more information about disk performance, see EBS performance.

Use scenarios

The following table describes the operations that you can perform on disks to meet your business requirements.

Business requirement References
Store application data
Resize a system disk or a data disk

For more information about disk expansion, see Overview.

For more information about how to expand a disk, see the following topics:
Persistent storage For more information, see the following topics:

Limits

  • We recommend that you mount a disk to an application by using a StatefulSet. If you use a Deployment to mount a disk, you must set the number of replicated pods to 1. If the number of replicated pods is not set to 1, multiple nodes may use the disk at the same time when replicated pods are scheduled to different nodes. In this case, you cannot prioritize the node where you want to mount or unmount a disk. When Deployment pods are restarted, disk mounting may fail due to the upgrade policy. Therefore, we recommend that you do not use a Deployment to mount a disk.
  • The type of disk must match the ECS instance types that are used in your cluster before you can mount a disk. For more information about the matching rules between disk types and ECS instance types, see Instance families.
  • You can mount at most 16 disks to each node. The maximum capacity of each disk is 32 TiB.

Billing rules

For more information, see Billing methods.

StorageClasses

StorageClass

ACK clusters support the following types of StorageClass:
  • alicloud-disk-efficiency: ultra disk.
  • alicloud-disk-ssd: standard SSD.
  • alicloud-disk-essd: ESSD.
  • alicloud-disk-available: a high-availability mode. In this mode, the system first attempts to create a standard SSD. If SSD resources are exhausted, the system attempts to create an ultra disk.
    Notice
    • For alicloud-csi-provisioner versions earlier than alicloud-csi-provisioner v1.14.8.39-0d749258-aliyun, the system first attempts to create an enhanced SSD.
    • If enhanced SSDs are out of stock, the system attempts to create a standard SSD.
    • If standard SSDs are out of stock, the system attempts to create an ultra disk.
  • alicloud-disk-topology: creates a disk in WaitForFirstConsumer mode.

The first four types of StorageClass are suitable for clusters that are created in single zones. The last type of StorageClass is suitable for clusters that are created across zones.

When you configure a StorageClass, the following rules determine the zone where the disk is created:
  • Specify volumeBindingMode: WaitForFirstConsumer in the StorageClass configurations to create a disk in the zone where the pod that uses the disk volume is deployed.
  • Specify volumeBindingMode: Immediate and specify a zone by setting the zoneId parameter in the StorageClass configurations to create a disk in the specified zone.
  • Specify volumeBindingMode: Immediate and specify multiple zones by setting the zoneId parameter in the StorageClass configurations to create a disk in one of the specified zones.
  • Specify volumeBindingMode: Immediate without setting the zoneId parameter in the StorageClass configurations to create a disk in the zone where csi-provisioner is deployed.

If your cluster is deployed across zones, we recommend that you specify volumeBindingMode: WaitForFirstConsumer in the StorageClass configurations. You can create a StorageClass based on the type of disk that is required.

Default StorageClass

Kubernetes provides the default StorageClass feature. If a PVC does not specify a StorageClass, the default StorageClass is used to provision a PV for the PVC. For more information, see Default StorageClass.

Note
  • The default StorageClass applies to all PVCs. Proceed with caution if your cluster has PVCs for multiple storage media. For example, the default StorageClass may create a disk PV for a PVC that defines an Apsara File Storage NAS (NAS) file system. Therefore, ACK clusters do not provide default StorageClasses. If you want to configure a default StorageClass, perform the following steps.
  • You can configure only one default StorageClass for each cluster. If you configure more than one default StorageClass for a cluster, all default StorageClasses become invalid.
  1. Configure the default StorageClass.
    Run the following command to set alicloud-disk-ssd as the default StorageClass:
    kubectl patch storageclass alicloud-disk-ssd -p '{"metadata": {"annotations":{"storageclass.kubernetes.io/is-default-class":"true"}}}'
    After the default StorageClass is configured, alicloud-disk-ssd is marked as (default)
    kubectl get sc

    Expected output:

    NAME                          PROVISIONER                       AGE
    alicloud-disk-ssd (default)   diskplugin.csi.alibabacloud.com   96m
  2. Use the default StroageClass.
    1. Use the following template to create a PVC without specifying a StorageClass:
      apiVersion: v1
      kind: PersistentVolumeClaim
      metadata:
        name: disk-pvc
      spec:
        accessModes:
        - ReadWriteOnce
        resources:
          requests:
            storage: 20Gi
      The cluster automatically creates a disk PV based on the default StorageClass alicloud-disk-ssd.
      kubectl get pvc

      Expected output:

      NAME       STATUS   VOLUME                   CAPACITY   ACCESS MODES   STORAGECLASS        AGE
      disk-pvc   Bound    d-bp18pbai447qverm3ttq   20Gi       RWO            alicloud-disk-ssd   49s
You can also run the following command to disable the default StorageClass:
kubectl patch storageclass alicloud-disk-ssd -p '{"metadata": {"annotations":{"storageclass.kubernetes.io/is-default-class":"false"}}}'