If the IO size is 64 KB or smaller, then use the hardware manufacturer's disk service times (use 15 ms if the disk service times are unknown). The larger the IO size, the longer the response times, but the more data can be transferred per second and vice versa. If there was no IO requests queued, then the disk has no work to do (not busy) and the performance of the disk can be considered good until it has work to do again.įinally, check the average IO sizes and response times of the outstanding requests. Keep in mind that the queue length alone doesn't determine if a disk is overwhelmed, but it does tell us if the disk has constant work to do. We are checking the queue length not because of the number of spindles, but because it means that the disk constantly has work to do. Disk Queue Length is a good choice because it calculates what the queue length might have been on average. The queue length can be quite erratic at times going from 0 to 1000 and back to 0 again in a quick succession, so the Avg. Disk Queue Length, % Idle Time, or % Disk Time. This can be done by monitoring the Current Disk Queue Length, Avg. Next, determine if the logical disks hosting the page files have outstanding IO requests by checking the queue length. 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.Clint Huffman, in Windows Performance Analysis Field Guide, 2015 Are the disks overwhelmed? 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, the disk can burst for approximately 3,130 seconds. 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). The maximum consumption rate is 16,000 tokens/s, which is the larger value between the disk burst IOPS and IOPS limit. Token consumption rate: This rate is calculated based on the I/O usage.Token production rate: This rate equals the disk IOPS limit, which is 6,800 tokens/s.In the following example, a 100-GB ultra-high I/O EVS disk is used, and the fixed burst duration is 1800s. The maximum IOPS and maximum throughput that a disk can reach also very with the data block size. However, this is not the case in practice. 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. The following uses an ultra-high I/O disk as an example. For data blocks of a large size, greater than or equal to 16 KB, the disk can reach the maximum throughput.For data blocks of a small size, such as 4 KB or 8 KB, the disk can reach the maximum IOPS.An EVS disk can achieve either the maximum IOPS or maximum throughput depending on which one is reached first. It does not represent the type of the underlying hardware devices.ĮVS disk performance is closely related with the data block size. The values in the table are calculated with 4 KB data blocks.Į: This API name indicates the value of the volume_type parameter in the EVS API. The single-queue access latency is the I/O latency when all I/O requests are processed sequentially. The IOPS increases by 50 for every one GB added until it reaches the maximum IOPS 50,000.ĭ: A single queue indicates that the queue depth or concurrency is 1. The throughput increases by 0.5 MB/s for every one GB added until it reaches the maximum throughput 350 MB/s.Ĭ: Take an ultra-high I/O disk as an example: The baseline IOPS is 1,800. For example, maximum IOPS = read IOPS + write IOPS.ī: Take an ultra-high I/O disk as an example: The baseline throughput is 120 MB/s. Read/write-intensive applications that require ultra-large bandwidthĪ: The maximum IOPS, maximum throughput, and burst IOPS limit are all calculated based on the sum of read and write operations.Highest performance disks excellent for enterprise mission-critical services as well as workloads demanding high throughput and low latencyĬost-effective disks designed for enterprise office applications requiring high throughput and low latencyĭisks suitable for commonly accessed workloadsĭisks suitable for less commonly accessed workloads Suitable for scenarios that require ultra-high bandwidth and ultra-low latency
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