:Previous-generation disks - local SSDs

When you use local SSDs, take note of the following items:

• Local SSDs bring risks of SPOFs because the disks are located on the physical machines that host the ECS instances associated with the disks. We recommend that you implement data redundancy at the application layer to ensure the availability of data.

• After you purchase an ECS instance that uses local SSDs, you cannot upgrade or downgrade the configurations of the instance, such as the number of CPU cores, the memory size, and the specifications of the local SSDs.

Local SSDs are located on the physical machines that host the ECS instances associated with the disks and provide storage capacities for the instances. Local SSDs have the following characteristics:

• Low latency: In most cases, local SSDs provide microsecond-level latency.

• High random I/O: Local SSDs deliver up to 12,000 random IOPS.

• High throughput: Local SSDs provide I/O throughput of up to 300 Mbit/s.

• Limited data durability: The durability of data stored on local SSDs varies based on the reliability of the associated physical machine. In this case, risks of SPOFs may arise. We recommend that you implement data redundancy at the application layer to ensure the availability of data.

• Storage capacity of up to 800 GB: A single local SSD can provide a storage capacity of up to 800 GB.

• Local SSDs are located on physical machines and cannot be separately attached to or unattached from ECS instances.

• After you purchase an ECS instance that uses local SSDs, you cannot upgrade or downgrade the configurations of the instance, such as the number of CPU cores, the memory size, and the specifications of the local SSDs.

Local SSDs provide low latency, high random I/O, and high throughput. Local SSDs are suitable for distributed and I/O-intensive applications that have redundancy capabilities in scenarios that do not require high data durability.

• You can use local SSDs for distributed and I/O-intensive applications such as NoSQL databases, massively parallel processing (MPP) data warehouses, and distributed file systems. Data redundancy is implemented on the applications in a distributed manner. Local SSDs can provide low latency, high random I/O, and high I/O throughput for the applications.

• You can use local SSDs to store the logs of large online applications. The applications can produce a large amount of log data and require high-performance storage. In addition, log data does not require highly reliable storage.

• You can use local SSDs as swap partitions in ECS instances. When applications that run on a Linux instance require more memory but the amount of memory allocated to the applications is exhausted, you can enable the swap space. After you enable the swap space, the Linux operating system can frequently swap in-use memory pages from the physical memory to the swap spaces regardless of whether the swap spaces are dedicated partitions of the existing file systems or swap files. The Linux operating system can also free up space for memory pages that require high access speeds.