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Disk Types and Performance

Updated at: Sep 02, 2021 GMT+08:00

EVS disks are classified into ultra-high I/O, general purpose SSD, high I/O, and common I/O disks based on the disk I/O performance. EVS disks differ in performance and price. Choose the disk type most appropriate for your applications.

EVS Disk Performance

EVS disk performance metrics include:
  • IOPS: Number of read/write operations performed by an EVS disk per second
  • Throughput: Amount of data read from and written into an EVS disk per second
  • Read/write I/O latency: Minimum interval between two consecutive read/write operations on an EVS disk
Table 1 EVS disk performance data

Parameter

Ultra-high I/O

General Purpose SSD

High I/O

Common I/O (Previous Generation Product)

Max. capacity

  • System disk: 1024 GB
  • Data disk: 32768 GB
  • System disk: 1024 GB
  • Data disk: 32768 GB
  • System disk: 1024 GB
  • Data disk: 32768 GB
  • System disk: 1024 GB
  • Data disk: 32768 GB

Short description

Highest performance disks excellent for enterprise mission-critical services as well as workloads demanding high throughput and low latency

Cost-effective disks designed for enterprise office applications requiring high throughput and low latency

Disks suitable for commonly accessed workloads

Disks suitable for less commonly accessed workloads

Typical application scenarios

  • Read/write-intensive applications that require ultra-large bandwidth
  • Transcoding services
  • I/O-intensive applications
    • NoSQL
    • Oracle
    • SQL Server
    • PostgreSQL
  • Latency-sensitive applications
    • Redis
    • Memcache
Mainstream high-performance, low-latency interactive applications
  • Enterprise office applications
  • Large-scale development and testing
  • Transcoding services
  • Web server logs
  • High-performance system disks, like container disks
Common workload applications
  • Common development and testing
Applications demanding large capacity, medium read/write speed, but having fewer transactions
  • Common office applications
  • Lightweight development and testing
  • Not recommended to be used as system disks

Max. IOPSa

50,000

20,000

5,000

2,200

Max. throughputa

350 MB/s

250 MB/s

150 MB/s

50 MB/s

Disk throughput

Throughput = Min. (350, 120 + 0.5 × Capacity) MB/s

Throughput = Min. (250, 100 + 0.5 × Capacity) MB/s

Throughput = Min. (150, 100 + 0.15 × Capacity) MB/s

Throughput = 50 MB/s

Burst IOPS limita

16,000

8,000

5,000

2,200

Disk IOPS

IOPS = Min. (50,000, 1,800 + 50 x Capacity)

IOPS = Min. (20,000, 1,800 + 12 x Capacity)

IOPS = Min. (5,000, 1,800 + 8 x Capacity)

IOPS = Min. (2,200, 500 + 2 x Capacity)

Single-queue access latency

1 ms

1 ms

1 ms to 3 ms

5 ms to 10 ms

API Nameb

SSD

GPSSD

SAS

SATA

a: The maximum IOPS, maximum throughput, and burst IOPS limit are all calculated based on the sum of read and write operations.

b: This API name indicates the value of the volume_type parameter in the EVS API. It does not represent the type of the underlying hardware device.

A large-capacity disk can achieve either the maximum IOPS or maximum throughput depending on which one is reached first. EVS disk performance is closely related with the data block size.

  • For data blocks of a small size, such as 4 KB or 8 KB, the disk can reach the maximum IOPS.
  • For data blocks of a large size, greater than or equal to 16 KB, the disk can reach the maximum throughput.

The following uses an ultra-high I/O disk as an example. According to the formula, when the size of an ultra-high I/O disk is greater than or equal to 964 GB, the disk theoretically can reach either the maximum IOPS 50,000 or the maximum throughput 350 MB/s. However, this is not the case in practice. The maximum IOPS and maximum throughput that a disk can reach also very with the data block size. For details, see Table 2.

Table 2 Maximum performance of ultra-high I/O EVS disk

Data Block Size (KB)

Max. IOPS

Max. Throughput (MB/s)

4

About 50,000

About 195

8

About 44,800

About 350

16

About 22,400

About 350

32

About 11,200

About 350

Disk IOPS Calculation Formula

Disk IOPS = Min. (Maximum IOPS, Baseline IOPS + IOPS per GB x Capacity)

The following example uses an ultra-high I/O EVS disk with a maximum IOPS of 50,000.
  • If the disk capacity is 100 GB, the disk IOPS is calculated as follows:

    Disk IOPS = Min. (50,000, 1,800 + 50 x 100)

    The disk IOPS is 6,800, the smaller value between 50,000 and 6,800.

  • If the disk capacity is 1,000 GB, the disk IOPS is calculated as follows:

    Disk IOPS = Min. (50,000, 1,800 + 50 x 1,000)

    The disk IOPS is 50,000, the smaller value between 50,000 and 51,800.

Disk Burst Capability and Principles

The burst capability allows a small-capacity disk to surpass the disk IOPS limit within a certain period of time. The IOPS limit indicates the performance of a single disk.

The burst capability is suitable for improving the server startup speed. Normally, system disks have small capacities. For example, if a 50-GB ultra-high I/O disk does not have the burst capability, its IOPS limit can reach only 4,300, calculated using the following formula: IOPS limit = Min. [50,000, (1,800 + 50 x Capacity). However, if the disk has the burst capability, its IOPS limit can burst up to 16,000.

The following example uses an ultra-high I/O EVS disk with the IOPS burst limit of 16,000.
  • If the disk capacity is 100 GB, the disk IOPS limit is 6,800. In this case, the disk maximum IOPS can reach 16,000 in a certain duration.
  • If the disk capacity is 1,000 GB, the disk IOPS limit is 50,000. In this case, the disk IOPS limit already exceeds its IOPS burst limit (16,000), and the disk does not need the burst capability.

The burst IOPS consumption and reservation principles are described as follows:

The burst capability is implemented based on a token bucket. The number of initial tokens in the bucket is calculated as follows:

Number of initial tokens = Burst duration x IOPS burst limit

In the following example, a 100-GB ultra-high I/O EVS disk is used, and the fixed burst duration is 1800s. Therefore, the number of initial tokens is 28,800,000 (1,800 x 16,000).
  • Token production rate: This rate equals the disk IOPS limit, which is 6,800 tokens/s.
  • Token consumption rate: This rate is calculated based on the I/O usage. Each I/O request consumes a token. The maximum consumption rate is 16,000 tokens/s, which is the larger value between the disk burst IOPS and IOPS limit.

Consumption principles

When the token consumption rate is greater than the production rate, the number of tokens decreases accordingly, and eventually the disk IOPS will be consistent with the token production rate (the IOPS limit). In this example, the disk can burst for approximately 3130 seconds [28,800,000/(16,000 - 6,800)].

Reservation principles

When the token consumption rate is smaller than the production rate, the number of tokens increases accordingly, enabling the disk to regain the burst capability. In this example, if the disk is suspended for approximately 4235 seconds (28,800,000/6,800), the token bucket will be filled up with tokens.

As long as there are tokens in the token bucket, the disk will have the burst capability.

Figure 1 shows the token consumption and reservation principles. The blue bars indicate the disk IOPS usage, the green dashed line represents the IOPS limit, the red dashed line indicates the IOPS burst limit, and the black curve indicates the changes of the number of tokens.
  • When the number of tokens is greater than zero, the disk IOPS can exceed 6,800 and has the capability to reach 16,000, the IOPS burst limit.
  • When the number of tokens is zero, the disk does not have the burst capability, and the maximum IOPS is 6,800.
  • When the disk IOPS is less than 6,800, the number of tokens starts to increase, and the disk can regain the burst capability.
Figure 1 Burst capability diagram

Performance Test Method

For details about how to test the EVS disk performance, see How Can I Test My Disk Performance.

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