Local disks are disks that are attached to the same physical machine that hosts their ECS instance. Local disks provide local storage and access for ECS instances. Local disks are cost-effective and provide high random IOPS, high throughput, and low latency.

Disk types

Note This topic provides information of local disks that are sold together with ECS instances. For more information about the performance of instance families using local SSDs and big data instance families, see Instance families.

Local disks are ideal for I/O-intensive workloads that require high cost-effectiveness. Alibaba Cloud provides the following two types of local disks:

  • NVMe SSD: This type of disks is ideal for instance families such as i2, i2g, i1, ga1, and gn5. i1 and i2 instance families are suitable for the following scenarios:
    • Services such as online gaming, e-commerce, live streaming, and media services that run I/O-intensive applications and require high I/O performance and low latency.
    • Services that require high I/O performance and a high-availability architecture at the application layer, such as NoSQL databases (including Cassandra, MongoDB, and HBase), MPP data warehouses, and distributed file systems.
  • SATA HDD: This type of disks is ideal for instance families such as d1ne and d1. These disks are the preferred storage media for industries with high requirements for big data computing, storage, and analysis, such as Internet and financial industries. The disks can fulfill the requirements of distributed computing services such as Hadoop, which have high requirements for storage performance, storage capacity, and internal bandwidth.

NVMe SSD performance

To obtain the standard performance data and measure the Quality of Service (QoS) of Alibaba Cloud local disks, you can test the bandwidth, IOPS, and latency of NVMe SSDs based on the performance metrics described in this topic. For more information about performance tests of NVMe SSDs, see Performance tests on Block Storage.

  • The following table describes the performance metrics of NVMe SSDs that i2 instances use.
    NVMe SSD performance metric Single disk performance Overall instance performance*
    ecs.i2.xlarge Other i2 instances
    Maximum capacity 894 GiB 1,788 GiB 1,788 × 8 GiB
    Maximum read IOPS 150,000 300,000 1,500,000
    Maximum read throughput 1 GB/s 2 GB/s 16 GB/s
    Maximum write throughput 0.5 GB/s 1 GB/s 8 GB/s
    Access latency Microsecond (μs)

    *Overall instance performance in the table applies only to ecs.i2.16xlarge. This performance represents the highest performance level for local storage in the i2 instance family.

  • The following table describes the performance metrics of NVMe SSDs that i1 instances use.
    NVMe SSD performance metric Single disk performance Overall instance performance***
    Maximum capacity 1,456 GiB 2,912 GiB
    Maximum IOPS 240,000 480,000
    Write IOPS** min{165 × Capacity, 240,000} 2 × min{165 × Capacity, 240,000}
    Read IOPS**
    Maximum read throughput 2 GB/s 4 GB/s
    Read throughput** min{1.4 × Capacity, 2,000} MB/s 2 × min{1.4 × Capacity, 2,000} MB/s
    Maximum write throughput 1.2 GB/s 2.4 GB/s
    Write throughput** min{0.85 × Capacity, 1,200} MB/s 2 × min{0.85 × Capacity, 1,200} MB/s
    Access latency Microsecond (μs)
    **The performance of a single NVMe SSD is calculated as follows:
    • Write IOPS: 165 IOPS per GiB, up to 240,000 IOPS
    • Write throughput: 0.85 MB/s per GiB, up to 1,200 MB/s

    ***Overall instance performance in the table applies only to ecs.i1.14xlarge. This performance represents the highest performance level for local storage in the i1 instance family.

SATA HDD performance

The following table describes the performance metrics of SATA HDDs.

SATA HDD performance metric Single disk performance Overall instance performance****
Maximum capacity 5,500 GiB 154,000 GiB
Maximum throughput 190 MB/s 5,320 MB/s
Access latency Millisecond (ms)

**** Overall instance performance in the table applies only to ecs.d1.14xlarge and ecs.d1ne.14xlarge instances. This performance represents the highest performance level for local storage in the d1 and d1ne instance families.

Billing methods

Local disks are billed along with the instances to which they are attached. For more information about ECS instance billing methods, seeSubscription and Pay-as-you-go.

Instructions

  • Local disks are attached to a single physical server, which increases the risk of single point of failure (SPOF). The reliability of data stored on local disks depends on the reliability of the physical server. To ensure data availability, we recommend that you implement data redundancy at the application layer. You can use deployment sets to distribute ECS instances across multiple physical machines to achieve high availability and disaster recovery. For more information, see Create a deployment set.
    Warning Data stored on local disks may be lost, for example, when a hardware failure occurs. We recommend that you do not use local disks for long-term data storage. If your applications do not have data reliability architecture, we recommend that you use cloud disks in your ECS instances for data reliability.
  • After you purchase an ECS instance that is equipped with a local disk, you must log on to the instance to partition and format the local disk. For more information, see Partition and format the local disk.
  • The following operations are not supported on a local disk:
    • Create a separate local disk
    • Use a snapshot to create a local disk
    • Attach a local disk
    • Detach and release a local disk separately
    • Resize a local disk
    • Reinitialize a local disk
    • Create a snapshot for a local disk
    • Use a snapshot to roll back a local disk

Disk initialization sequence

When you create an ECS instance that is equipped with local disks, all disks are initialized based on the following rules:
  • Rule 1: If the specified image does not have data disk snapshots, the local disks are initialized prior to the cloud disks that are created along with the ECS instance.
  • Rule 2: If the specified image has data disk snapshots, the initialization sequence of the data disks corresponds to what the snapshots have retained. The initialization sequence of the remaining disks is subject to Rule 1.
For example, for a Linux image that contains snapshots of two data disks, the disks are initialized in the following sequence.
  • If the original device names of the two data disks are /dev/xvdb and /dev/xvdc, Alibaba Cloud first allocates /dev/xvdb and /dev/xvdc to specified data disks in the image. The system disk is initialized first. Then, the initialization proceeds in the following sequence: data disk 1 specified in the image, data disk 2 specified in the image, local disk 1, local disk 2, cloud disk 1, cloud disk 2, and cloud disk N. This is shown in the following figure.Rule 2 - Schematic 1
  • If the original device names of the two data disks are /dev/xvdc and /dev/xvdd, Alibaba Cloud first allocates /dev/xvdc and /dev/xvdd to specified data disks in the image. The remaining device names are preferentially allocated to the local disks. The system disk is initialized first. Then, the initialization proceeds in the following sequence: local disk 1, data disk 1 specified in the image, data disk 2 specified in the image, local disk 2, cloud disk 1, cloud disk 2, and cloud disk N. This is shown in the following figure.Rule 2 - Schematic 2

Lifecycle

A local disk has the same lifecycle as the instance to which it is attached. For more information, see ECS instance lifecycle.

Impact of instance operations on the data stored on local disks

The following table describes the impact of instance operations on the data stored on local disks.

Instance operation Data stored on the local disk Local disk
Restart the operating system, restart the instance by using the ECS console, or forcibly restart the instance. Retained Retained
Shut down the operating system, , stop the instance by using the ECS console, or forcibly stop the instance. Retained Retained
Automatically restore the instance. Erased Released
Release the instance. Erased Released
A subscription instance is stopped when it expires or a pay-as-you-go instance is stopped when there is an overdue payment. However, the instance has not been released. Retained Retained
A subscription instance is stopped when it expires or a pay-as-you-go instance is stopped when there is an overdue payment. After that, the instance is released. Erased Released
Renew an expired subscription instance. Retained Retained
Reactivate a pay-as-you-go instance that is stopped due to an overdue payment. Retained Retained

References

For more information about phased-out local SSDs, see Ephemeral SSDs.