BMSs support Elastic Volume Service (EVS) disks. BMSs can be started from EVS disks and quickly provisioned. EVS disks attached to BMSs can be shared disks. If a shared disk is attached to a BMS, the BMS shares this disk with other BMSs or ECSs.
EVS Disk Types
BMSs support the following types of EVS disks for storing data:
- Common I/O: EVS disks of this type deliver a maximum of 1000 IOPS. This disk type is suitable for application scenarios that require large capacity, a medium read/write rate, and fewer transactions, such as enterprises' office applications and small-scale test.
- High I/O: EVS disks of this type deliver a maximum of 3000 IOPS and a minimum of 6 ms read/write latency. This disk type is designed to meet the needs of mainstream high-performance, high-reliability application scenarios, such as enterprise applications, large-scale development and test, and web server logs.
- Ultra-high I/O: EVS disks of this type deliver a maximum of 20,000 IOPS and a minimum of 1 ms read/write latency. This disk type is excellent for ultra-high I/O, ultra-high bandwidth, and intensive read/write application scenarios. For example, the distributed file systems in the HPC scenarios or NoSQL and relational databases in I/O-intensive scenarios.
EVS Disk Performance
The key indicators of EVS disk performance include read/write I/O latency, IOPS, and throughput.
- IOPS: number of read/write operations performed by an EVS disk per second
- Throughput: amount of data successfully transmitted by an EVS disk per second, that is, the amount of data read from and written into an EVS disk
- Read/write I/O latency: minimum interval between two consecutive read/write operations of an EVS disk
For details about EVS disk performance indicators, see Elastic Volume Service User Guide.
EVS Disk Device Types
The BMS only supports the Small Computer System Interface (SCSI) EVS disks.
You can create EVS disks for which Device Type is SCSI on the management console. These EVS disks support transparent SCSI command transmission, allowing BMS OS to directly access underlying storage media. Besides basic read/write SCSI commands, such EVS disks also support advanced SCSI commands.
The BMS image OS is preinstalled with the driver required for using SCSI device type disks, and you do not need to install the driver explicitly. For details about how to install drivers, you can see section "Installing the SDI Card Driver" in the Bare Metal Server Private Image Creation Guide.