Local storage for cloud servers¶
Cloud servers are generally created with a given amount of local storage available to them in the form of one or more virtual hard disks. To best use this local storage, you should understand the different types of storage that are available.
Local storage technologies and terminology¶
The virtual hard disks allocated to a cloud server are backed by one of several different physical technologies, depending on how you choose to configure the server. Each storage technology has specific performance and cost characteristics.
Following is a high-level comparison of the technologies:
|Server type||Speed||Cost (relative)|
|SATA (Standard Cloud Servers)||Average||Lowest|
|SSD (I/O and General Purpose Cloud Servers)||Fast||Medium|
Measuring local storage performance: IOPS¶
One way to compare the performance metrics of storage is by using Input/Output Operations per Second (IOPS). IOPS reports the maximum number of operations per second the storage can handle. For the purpose of calculating IOPS, an operation is typically a read or write of data.
Several factors can cause the effective measured IOPS capability of a storage medium to fluctuate, including system load, background operations, and traffic from other virtual machines residing on the same physical disks. Because of this, consider any IOPS measurements you obtain as describing the upper limit of each local storage option's range, identifying the highest possible IOPS that the device can process. Although this provides information about performance, it is important to remember that many factors can affect the IOPS rate during operation. IOPS is most useful as a basis of comparison if you can control all other factors and run identical workloads on systems that differ only in their storage configuration.
You can see the results of a performance experiment comparing Rackspace storage technologies at Determining Optimal Storage based on IOPS. In that experiment, Cloud Block Storage on SSD performed better than any other option tested. In a white paper on Cloud Block Storage (CBS) Benchmarking, performance quadrupled using Cloud Block Storage with SSD as compared to Cloud Block Storage with SATA.
Local storage types associated with Cloud Servers flavors¶
Choosing a flavor class for your server also means choosing what kind of local storage is available to that server.
- For Compute and Memory flavor classes, storage is entirely backed by Cloud Block Storage.
- For I/O and General Purpose flavor classes, storage is RAID 10 SSD.
- For Standard flavor classes, storage is RAID 10 SATA hard disk drives.
SATA local storage¶
Also known as spinning disk, Serial Advanced Technology Attachment (SATA) disks are the traditional hard drives with physical platters with which most people are familiar. Because of efficiencies in engineering and manufacturing over time, they can provide large capacities at relatively low prices. However, because of the physical spinning platters and moving write heads of SATA disks, they are slower than newer technologies such as SSD in many situations.
SSD local storage¶
Solid State Disk (SSD) uses persistent RAM technology to store data. Because SSD has no moving parts, locating and reading any given bit of data from the disk is extremely fast when compared to SATA, which is delayed by the movements of platters and write heads. This speed comes at a literal cost because SSD components are more expensive than SATA components.
Local storage types associated with OnMetal flavors¶
OnMetal Cloud Servers are backed by storage that complies with the Peripheral Component Interconnect (PCI) local bus standard.
OnMetal Cloud Servers offer the benefits of the following kinds of configuration:
- the elasticity of cloud computing
- the consistent performance of colocated hosting
When you create a server, if you make it an OnMetal server, you can choose one of the following flavor classes designed to support specific workloads:
- OnMetal I/O, optimized for databases
- OnMetal Memory, optimized for caching
- OnMetal Compute, optimized for CPU-intensive workloads
Every OnMetal flavor class provides 32 GB for the system disk. The OnMetal I/O flavor class also provides Dual 1.6 TB PCIe flash cards for the data disk.
For more information about OnMetal, see the following resources: