Cloud disk persistent volumes

Features

Disks are block storage products offered by Alibaba Cloud for Elastic Compute Service (ECS) instances. They provide low latency, high performance, persistence, and high reliability. Disks use a distributed triplicate mechanism to ensure data reliability for ECS instances. Your data is automatically replicated within a zone to prevent data unavailability caused by hardware failures and to protect your services from component failures. For more information, see Disk overview.

• ESSD AutoPL disks: You can configure the burst performance and provisioned performance of ESSD AutoPL disks based on your business requirements. ESSD AutoPL disks inherit the features and performance of enhanced SSDs (ESSDs) and provide the capability of decoupling disk capacity from disk performance. For more information, see ESSD AutoPL disks.

  We recommend that you use ESSD AutoPL disks in the following scenarios:

  • Scenarios for which ESSDs are suitable, such as large-sized online transactional processing (OLTP) databases, NoSQL databases, and Elasticsearch, Logstash, and Kibana (ELK) distributed logs.

  • Scenarios in which disk performance needs to be increased without extending disk capacity.

  • Scenarios in which business workloads significantly fluctuate and disks need to burst their performance when workload spikes occur.

• ESSDs: ESSDs are based on the next-generation distributed block storage architecture and utilize 25 Gigabit Ethernet and remote direct memory access (RDMA). Each ESSD has low one-way 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 OLTP databases, NoSQL databases, and 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.

• ESSD Entry disks: ESSD Entry disks provide enterprise-grade features and data protection capabilities. We recommend that you use ESSD Entry disks as system disks or for scenarios such as development and testing.

  Note

  You can attach ESSD Entry disks only to instances of the u1 and e instance families. For information about the instance families, see the u1, universal instance family section in the "Universal instance families" topic and the e, economy instance family section in the "Shared instance families" topic.

• 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.

Scenarios

You can perform the following operations on disks as needed:

Limits

• Disks are non-shared storage. If multi-attach is not enabled for a disk, it can be mounted to only one pod at a time. For more information about multi-attach, see Use the multi-attach and reservation features of NVMe disks.

• You can mount a disk only to a pod that resides in the same zone as the disk. Cross-zone mounting is not supported.

• The ECS instance types to which a cloud disk can be attached depend on the category of the disk.

  When you mount a disk volume to a pod, make sure that the instance type of the ECS instance on which the pod runs supports the category of the disk that you want to mount. For more information about the matching rules between disk categories and ECS instance types, see Overview of instance families.

Billing

• Only pay-as-you-go disks can be attached. Subscription disks are not supported. If you change the billing method of an ECS instance in a cluster from pay-as-you-go to subscription, do not change the billing method of the disk to subscription. Otherwise, the disk cannot be attached. You can purchase Storage Capacity Units (SCUs) to reduce disk costs. For more information about SCU billing, see Storage Capacity Unit (SCU).

• You are not charged for StorageClass itself. However, disks that are automatically created by a StorageClass are billed as pay-as-you-go disks.

• For information about disk billing items, see Elastic Block Storage billing. For information about disk pricing, see Detailed Pricing.

For more information, see Billing.

StorageClass

If the number of PersistentVolumeClaim (PVC) requests is large, many Persistent Volumes (PVs) must be created. This increases maintenance costs for operations and maintenance (O&M) engineers. To address this, Kubernetes provides a mechanism called StorageClass for automatic PV creation.

ACK provides the following default StorageClasses.

When you create a disk using a StorageClass, the zone is selected based on the following rules:

• If the StorageClass is configured with volumeBindingMode: WaitForFirstConsumer, the disk is created in the same zone as the pod that is associated with the PVC.

• If the StorageClass is configured with volumeBindingMode: Immediate and the zoneId parameter is set to a single zone, the disk is created in that zone.

• If the StorageClass is configured with volumeBindingMode: Immediate and the zoneId parameter is set to multiple zones, a zone is selected from the specified zones in a round-robin manner to create the disk.

Therefore, if you have a multi-zone cluster, use a StorageClass in WaitForFirstConsumer mode. You can create a StorageClass for the required disk type.

Default StorageClass

Kubernetes provides a Default StorageClass mechanism. You can use a Default StorageClass to create a data volume when a StorageClass is not specified in the PVC. For more information, see Default StorageClass.

1. Run the following command to configure the StorageClass (alicloud-disk-ssd) as a Default StorageClass.

   kubectl patch storageclass alicloud-disk-ssd -p '{"metadata": {"annotations":{"storageclass.kubernetes.io/is-default-class":"true"}}}'

   Query the StorageClasses in the cluster. You can see that (default) is added to the name of alicloud-disk-ssd.

   kubectl get sc

   Expected output:

   NAME                          PROVISIONER                       AGE
   alicloud-disk-ssd (default)   diskplugin.csi.alibabacloud.com   96m

2. Use the Default StorageClass.

   Use the following template to create a PVC without a specified StorageClass.

   apiVersion: v1
   kind: PersistentVolumeClaim
   metadata:
     name: disk-pvc
   spec:
     accessModes:
     - ReadWriteOnce
     resources:
       requests:
         storage: 20Gi

   The cluster automatically creates a disk volume (PV) and uses 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

kubectl patch storageclass alicloud-disk-ssd -p '{"metadata": {"annotations":{"storageclass.kubernetes.io/is-default-class":"false"}}}'