Disk Types and Performance
EVS disks are classified into the following types by I/O performance: Extreme SSD, General Purpose SSD V2, Ultra-high I/O, General Purpose SSD, High I/O, and Common I/O. EVS disks differ in performance and price. Choose the disk type most appropriate for your applications.
Extreme SSD EVS disks use the congestion control algorithms for Remote Direct Memory Access (RDMA) deployments. An extreme SSD disk can reach up to 1,000 MiB/s of throughput and with extremely low single-channel latency.
EVS Performance
- 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
Parameter |
Extreme SSD |
General Purpose SSD V2 |
Ultra-high I/O |
General Purpose SSD |
High I/O |
Common I/O (Previous Generation Product) |
---|---|---|---|---|---|---|
Max. capacity (GiB) |
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Short description |
Superfast disks for workloads demanding ultra-high bandwidth and ultra-low latency |
SSD-backed disks allowing for tailored IOPS and throughput and targeting for transactional workloads that demand high performance and low latency |
High performance disks excellent for enterprise mission-critical services as well as workloads demanding high throughput and low latency |
Cost-effective disks designed for enterprise applications with medium performance requirements |
Disks suitable for commonly accessed workloadsf |
Disks suitable for less commonly accessed workloads |
Typical workloads |
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Common development and test environments |
Applications demanding large capacity, medium read/write speed, but having fewer transactions
|
Max. IOPSa |
128,000 |
128,000 |
50,000 |
20,000 |
5,000 |
2,200 |
Max. throughputa (MiB/s) |
1,000 |
1,000 |
350 |
250 |
150 |
50 |
Burst IOPS limita |
64,000 |
N/A |
16,000 |
8,000 |
5,000 |
2,200 |
Disk IOPSc |
Min. [128,000, 1,800 + 50 x Capacity (GiB)] |
You preconfigure an IOPS ranging from 3,000 to 128,000. This IOPS must also be less than or equal to 500 times the capacity (GiB). |
Min. [50,000, 1,800 + 50 x Capacity (GiB)] |
Min. [20,000, 1,800 + 12 x Capacity (GiB)] |
Min. [5,000, 1,800 + 8 x Capacity (GiB)] |
Min. [2,200, 500 + 2 x Capacity (GiB)] |
Disk throughputb (MiB/s) |
Min. [1,000, 120 + 0.5 × Capacity (GiB)] |
You preconfigure a throughput ranging from 125 to 1,000. This throughput must also be less than or equal to the IOPS divided by 4. |
Min. [350, 120 + 0.5 × Capacity (GiB)] |
Min. [250, 100 + 0.5 × Capacity (GiB)] |
Min. [150, 100 + 0.15 × Capacity (GiB)] |
50 |
Single-queue access latencyd (ms) |
Sub-millisecond |
1 |
1 |
1 |
1–3 |
5–10 |
API Namee |
ESSD |
GPSSD2 |
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. For example, maximum IOPS = read IOPS + write IOPS.
b: Take ultra-high I/O for example: The baseline throughput is 120 MiB/s. The throughput increases by 0.5 MiB/s for every one GiB added until it reaches the maximum throughput 350 MiB/s.
c: Take ultra-high I/O for example: The baseline IOPS is 1,800. The IOPS increases by 50 for every one GiB added until it reaches the maximum IOPS 50,000.
d: A single queue indicates that the queue depth or concurrency is 1. The single-queue access latency is the I/O latency when all I/O requests are processed sequentially. The values in the table are calculated with 4 KiB data blocks.
e: This API name is the value of the volume_type parameter in the EVS API. It does not represent the type of the underlying hardware device.
f: High I/O disks (except for those created in dedicated storage pools) are HDD-backed disks. They are suitable for applications with commonly accessed workloads. The baseline throughput of a high I/O disk is 40 MiB/s per TiB, and the maximum throughput of a high I/O disk is 150 MiB/s. If your applications have high workloads, it is recommended that you choose SSD-backed disks which have higher specifications.
EVS disk performance is closely related with the data block size:
- If data blocks are of the same size, a disk can achieve either the maximum IOPS or maximum throughput depending on which one is reached first.
- If data blocks are of different sizes, the maximum performance metric that a disk can achieve varies:
- For small data blocks, such as 4 KiB or 8 KiB, a disk can reach the maximum IOPS.
- For data blocks greater than or equal to 16 KiB, a disk can reach the maximum throughput.
Table 2 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 GiB, the disk theoretically can reach either the maximum IOPS 50,000 or the maximum throughput 350 MiB/s. However, this is not the case in practice. The maximum IOPS and maximum throughput that a disk can reach also vary with the data block size.
Disk IOPS Calculation Formula
Disk IOPS = Min. (Maximum IOPS, Baseline IOPS + IOPS per GiB x Capacity)
This calculation formula does not apply to General Purpose SSD V2 disks.
For a General Purpose SSD V2 disk: You preconfigure an IOPS ranging from 3,000 to 128,000. This IOPS must also be less than or equal to 500 times the capacity (GiB).
If the disk capacity is 100 GiB, the disk IOPS is calculated as follows: Disk IOPS = Min. (50,000, 1,800 + 50 × 100)
The disk IOPS is 6,800, the smaller of the two values (50,000 and 6,800).
If the disk capacity is 1,000 GiB, the disk IOPS is calculated as follows: Disk IOPS = Min. (50,000, 1,800 + 50 × 1,000)
The disk IOPS is 50,000, the smaller of the two values (50,000 and 51,800).
Disk Burst Capability and Principles
EVS disks have burst capability, which allows a small-capacity disk to surpass its maximum IOPS within a certain period of time. This IOPS applies to each disk individually.
Disks with burst capability are well-suited for speeding up server startup. In most cases, system disks are fairly small, so their basic IOPS is fairly low. For example, the IOPS of a 50-GiB ultra-high I/O disk without burst capability can only reach up to 4,300 IOPS (Min. (50,000, 1,800 + 50 x Capacity)). But with burst capability, its IOPS can burst up to 16,000.
- If the disk capacity is 100 GiB, the disk has a maximum IOPS of 6,800, but it can burst to 16,000 IOPS in a certain duration.
- If the disk capacity is 1,000 GiB, the disk has a maximum IOPS of 50,000. The disk maximum IOPS already exceeds its burst IOPS 16,000, and the disk does not use the burst capability.
The following describes the burst IOPS consumption and reservation.
A token bucket is used to handle burst I/O operations. The number of initial tokens in the bucket is calculated as follows:
Number of initial tokens = Burst duration x IOPS burst limit
- Token production rate: This rate equals the disk maximum IOPS, 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 of the disk burst IOPS and the maximum IOPS.
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 maximum IOPS). In this example, the disk can burst for approximately 3,130 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 4,235 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 has the burst capability.
- 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 disk IOPS can reach up to 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.
Performance Test Method
For details about how to test the EVS disk performance, see How Do I Test My Disk Performance?
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