Local disks are located on the physical servers (host machines) that ECS instances are hosted on. They provide temporary block level storage for instances, featuring low latency, high random IOPS, and high I/O throughput. They are designed for business scenarios requiring high storage I/O performance.
Because a local disk is attached to a single physical server, the data reliability depends on the reliability of the physical server, which may cause single points of failure. We recommend that you implement data redundancy at the application layer to guarantee data availability.
|Using a local disk for data storage can carry a risk of data loss in some cases, such as when the host machine is down. Therefore, never store any business data that requires long-term persistence on a local disk. If no data reliability architecture is available for your application, we strongly recommend that you build your ECS with elastic block storage.|
Currently, Alibaba Cloud provides two types of local disks:
Local NVMe SSD: This disk is used together with instances of the following type families: i2, i1, gn5, and ga1. The instance type families i1 and i2 apply to the following scenarios:
- Online games, e-businesses, live videos, media, and other industries that provide online businesses and have low latency and high I/O performance requirements on block level storage for I/O-intensive applications.
- Business scenarios that have high requirements on the storage I/O performance and availability of the application layer, such as NoSQL non-relational databases, MPP data warehouses, and distributed file systems.
Local SATA HDD: This disk is used together with instances of the d1ne and the d1 type families. It is applicable to the Internet, finance, and other allied businesses that require big data computing and storage analysis for massive data storage and offline computing business scenarios. It fully meets the needs of distributed computing business models represented by Hadoop in multiple aspects, such as instance storage performance, capacity, and intranet bandwidth.
Performance of local NVMe SSD
The following table lists the performance of local NVMe SSD of an i1 ECS instance.
|Parameters||Local NVMe SSD|
Single disk: 1,456 GiB
Total: 2,912 GiB
Single disk: 240,000
Read throughput per disk: 2 GBps
Total read throughput: 4 GBps
Write throughput per disk: 1.2 GBps
Total write throughput: 2.4 GBps
|Single-disk performance*||Write performance:
|Access latency||In microseconds|
* Explanation on single disk performance calculation formulas:
- Write IOPS for a single local NVMe SSD: 165 IOPS for each GiB, up to 240,000 IOPS.
- Write throughput for a single local NVMe SSD: 0.85 MBps for each GiB, up to 1,200 Mbit/s.
Performance of local SATA HDD
The following table lists the performance of local SATA HDD of a d1ne or d1 ECS instance.
|Parameters||Local SATA HDD|
Single disk: 5,500 GiB
Total capacity per instance: 154,000 GiB
Single disk: 190 MBps
Total throughput per instance: 5,320 MBps
|Access latency||In milliseconds|
A local disk has the same lifecycle as the instance that it is attached to:
- You can create a local disk only when creating an instance that has local storage. The capacity of a local disk is determined by the ECS instance type. You cannot increase or decrease it.
- When the instance is released, the local disk is released with it.
Operations on an instance affect the data on the local disk
The following table shows how operations on an instance that has local storage affect the state of the data on the local disk.
|Operation||State of the data on the local disk||Description|
|Restart within the operating system/restart or force restart in the ECS console||Retained||Both the storage volumes and data on the local disk are retained.|
|Shut down within the operating system/Stop or force stop in the ECS console||Retained||Both the storage volumes and data on the local disk are retained.|
|Release in the ECS console||Erased||The storage volumes on the local disk are erased and the data on it is not retained.|
|Downtime migration||Erased||The storage volumes on the local disk are erased and the data on it is not retained.|
|Out-of-service (Before the computing resources of an instance is released)||Retained||Both the storage volumes and data on the local disk are retained.|
|Out-of-service (After the computing resources of an instance is released)||Erased||The storage volumes on the local disk are erased and the data on it is not retained.|
If your ECS instance comes with local disks, you must connect to the instance to format the disk. Unlike cloud disks, you cannot perform the following operations on local disks:
- Independently creating an empty local disk or creating a local disk from a snapshot.
- Attaching a local disk in the ECS console.
- Detaching and releasing a local disk.
- Increasing the size of a local disk.
- Re-initializing a local disk.
- Creating a snapshot for a local disk and using the snapshot to roll back the local disk.