As a new instance type of ApsaraDB for RDS, dedicated instances feature fixed computing capabilities, storage space, and IO performance. It differs from other instance types in terms of resource allocation strategies. With more stable performance, a dedicated instance is the best option for business scenarios where a database-centric system is used, such as finance, e-commerce, government, medium- and large-sized Internet businesses.
Dedicated instances have multiple specification types. For more information, see Instance type list. Dedicated-host instances have the top-level configurations among dedicated instances. You can change the instance configurations as needed. Configuration changes are free of restrictions, which means configuration changes are allowed across different instance types.
- With the help of the OS (Linux/Windows) kernel, RDS isolates computing resources of instances located on different physical servers. A dedicated instance uses a slightly different CPU allocation strategy from a common instance. A number of fully dedicated CPU cores and threads are assigned to the dedicated instance to ensure long-term stability and predictability in computing performance. This avoids noisy neighborhood on the physical server.
- A dedicated instance has a reserved storage space. As compared with a common instance, the dedicated instance can fully avoid instance migration across physical machines caused by disk capacity increase of your instance or other instances to provide higher stability. Furthermore, the dedicated instance supports hot standby, so you can fail over at any time in case of disk failure on one instance, guaranteeing the availability of the instance. After the failover, you can change the host in host replacement mode. The process is transparent and does not affect your services.
It is not likely to make direct comparison between dedicated and common instances, because their metrics do not fully match. However, to help make purchase decisions, we select two similar specifications for a cost-effectiveness analysis.
|Type||Type ID||CPU/Memory||Disk space||Maximum number of connections||Maximum IOPS||Monthly price (effective before January 2017)|
|Common instances||rds.mysql.m1.medium||4-core 16 GB||500 GB||4000||7000||2,100 RMB|
|Dedicated instances||mysql.x8.large. 2||4-core 32 GB||500 GB||5000||9000||3,650 RMB|
The above table shows that a dedicated instance costs 70% more than a common instance, but it offers twice the memory capacity as the common instance, 25% more in the maximum number of connections, and 28% more in the maximum IOPS. In addition, it has stable CPU computing performance. Therefore, the dedicated instance provides higher overall cost-effectiveness. For more information about the prices of dedicated instances, see Pricing.