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Container Service for Kubernetes:Disk volume overview

Last Updated:Jun 06, 2023

You can create volumes to mount Alibaba Cloud disks to a Container Service for Kubernetes (ACK) cluster. You can use the Contain Storage Interface (CSI) plug-in provided by Alibaba Cloud to mount disks by creating persistent volumes (PVs) and persistent volume claims (PVCs). PVs can be statically or dynamically provisioned. This topic describes the features, disk types, use scenarios, limits, and billing rules of disk volumes.


Alibaba Cloud disks are block-level data 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 errors, data in the zone is automatically replicated to an unaffected disk in another zone to ensure data availability.

  • Enhanced SSDs (ESSDs): ESSDs are based on the next-generation distributed block storage architecture and use the 25 Gigabit Ethernet and remote direct memory access (RDMA) technologies. ESSDs provide low-latency input and output. Each ESSD can provide 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 for scenarios such as development and testing.

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

Disk types

ItemESSD AutoPL diskESSDStandard SSDUltra diskBasic disk
Capacity range per disk (GiB)40~32,7681261~32,768461~32,76820~32,76840~32,76820~32,76820~32,7685~2,000
Maximum IOPS1,000,0001,000,000100,00050,00010,00025,000 5,000Several hundreds
Maximum throughput (MB/s)4,0964,000750350180300 14030~40
Formula for calculating the IOPS per disk
  • Baseline performance: min{1,800 + 50 × Capacity, 50,000}
  • Provisioned performance: min{Provisioned IOPS, 50,000}
  • Burst performance: min{IOPS supported by the instance type, 1,000,000}
min{1,800 + 50 × Capacity, 1,000,000}min{1,800 + 50 × Capacity, 100,000}min{1,800 + 50 × Capacity, 50,000}min{1,800+12 × Capacity, 10,000}min{1,800 + 30 × Capacity, 25,000}min{1,800 + 8 × Capacity, 5,000}None
Formula for calculating the throughput per disk (MB/s)
  • Baseline performance: min{120 + 0.5 × Capacity, 350}
  • Provisioned performance: min{16 KB × Provisioned IOPS/1,024, Maximum throughput per disk}
  • Burst performance: min{Throughput supported by the instance type, 4 GB/s}
min{120 + 0.5 × Capacity, 4,000}min{120 + 0.5 × Capacity, 750}min{120 + 0.5 × Capacity, 350}min{100 + 0.25 × Capacity, 180}min{120 + 0.5 × Capacity, 300}min{100 + 0.15 × Capacity, 140}None
Average one-way random write latency in milliseconds (block size = 4 KB)
API parameter valuecloud_autocloud_essdcloud_essdcloud_essdcloud_essdcloud_ssdcloud_efficiencycloud

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


Store application data

Resize a system disk or a data disk

For more information, see Disk resizing.

Back up disk data

For more information, see Use volume snapshots created from disks.

Encrypt disk data

For more information, see Encryption overview.

For more information, see Encrypt disk volumes.

Usage notes

  • Alibaba Cloud disks cannot be shared. Each disk can be mounted only to one pod.

  • We recommend that you mount a disk 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.

  • When you mount a disk volume, if the securityContext.fsgroup parameter is set in the application template, kubelet performs the chmod and chown operations after the volume is mounted. This increases the mounting time. For more information about how to reduce the mounting time, see Why does it require a long time to mount a NAS volume? and Why does it require a long period of time to mount an OSS volume?.

Billing rules

  • Only pay-as-you-go disks can be mounted. If you change the billing method of an ECS instance in the cluster from pay-as-you-go to subscription, you cannot change the billing method of its disks to subscription. Otherwise, the disks cannot be mounted to the cluster.

  • For information about the billable items of disks, see EBS billing. For more information about the pricing of disks, visit the ECS product page.

  • If the disk that you want to mount does not support the subscription billing method, you can purchase storage capacity units (SCUs) to reduce the cost. For more information about SCUs, see Introduction to SCUs.

For more information, see Billing.


If you create a large number of PVCs, you must also create a large number of PVs. This increases the workloads of O&M engineers. To solve this issue, Kubernetes provides the StorageClass object that you can use to enable automatic PV creation.


ACK clusters support the following types of StorageClass:

  • alicloud-disk-efficiency: ultra disk.
  • alicloud-disk-ssd: standard SSD.
  • alicloud-disk-essd: ESSD.
  • alicloud-disk-topology: creates a disk in WaitForFirstConsumer mode.

  • alicloud-disk-topology-alltype: attempts to create a disk based on the following disk types in a round robin manner: cloud_essd (ESSD), cloud_ssd (SSD), and cloud_efficiency (ultra disk). The disk is created in WaitForFirstConsumer mode and therefore is compatible with multi-zone clusters.

The first three types of StorageClass are suitable for clusters that are created in single zones. The last two types 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:

  • If you set volumeBindingMode: WaitForFirstConsumer in the StorageClass configuration, a disk is created in the zone where the pod is deployed.

  • If you set volumeBindingMode: Immediate and specify only one zone in the zoneId parameter of the StorageClass configuration, a disk is created in the specified zone.

  • If you set volumeBindingMode: Immediate and specify multiple zones in the zoneId parameter of the StorageClass configuration, the system attempts to create a disk in the specified zones in a round robin manner.

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

Default StorageClass

Kubernetes provides the default StorageClass feature. If no StorageClass is specified for a persistent volume claim (PVC), the default StorageClass is used to provision a persistent volume (PV) for the PVC. For more information, see Default StorageClass.

  • The default StorageClass takes effect on all PVCs. Proceed with caution if your cluster uses PVCs of different storage types. For example, the default StorageClass may create a disk PV for a PVC that defines a 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 a default StorageClass.

    Run the following command to set alicloud-disk-ssd as the default StorageClass:

    kubectl patch storageclass alicloud-disk-ssd -p '{"metadata": {"annotations":{"":"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)   96m
  2. Use the default StorageClass.

    1. Use the following template to create a PVC with no StorageClass specified

      apiVersion: v1
      kind: PersistentVolumeClaim
        name: disk-pvc
        - ReadWriteOnce
            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":{"":"false"}}}'