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Dell Unity™ Family Unisphere® Command Line Interface User Guide

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Manage I/O limits

An I/O policy allows you to limit throughput and bandwidth, providing for more predictable performance in system workloads, that is, between hosts and applications and storage resources.

The following table lists the attributes for I/O limits:

Table 1. I/O limit attributes
Attribute	Description
ID	ID of the I/O limit.
Name	Name of the I/O limit.
Description	Brief description of the I/O limit.
Shared	Whether the I/O limit is shared, that is, whether settings are enforced on the sum of all the storage resources that have this policy or on each individual storage resource. Values are one of the following: yes no (default)
Paused	Whether the defined I/O limit policy is paused. Values are one of the following: yes no
Type	Whether the I/O limit is absolute or density based. Values are one of the following: absolute (default) density
Maximum IOPS	Maximum I/O operations per second for an absolute limit policy.
Maximum KBPS	Maximum KB per second for an absolute limit policy.
Maximum IOPS per GB	Maximum IOPS per GB of size for the attached object. This is applicable only when the policy type is density based. The effective limit is the product of the maximum IOPS and the size in GB of the attached object.
Maximum KBPS per GB	Maximum KBPS per GB of size for the attached object. This is applicable only when the policy type is density based. The effective limit is the product of the maximum KBPS and the size in GB of the attached object.
Burst rate	Amount of traffic over the base I/O limit that can occur during the burst time, expressed as a percentage of the base limit. Burst time and burst frequency must also be specified. Value is 1-100.
Burst time	Number of minutes during which traffic may exceed the base limit. Burst rate and burst frequency must also be specified. Use the following format: <`value`><`qualifier`> where: `value` minutes — Number of minutes within the range 1 - 60. `qualifier` m — Indicates minutes. NOTE:This setting is not a hard limit and is used only to calculate the extra I/O operations allocated for bursting. The actual burst time depends on I/O activity and may be longer than defined when activity is lower than the allowed burst rate.
Burst frequency	Number of hours between the beginning of one burst and the following burst. Burst rate and burst time must also be specified. Use the following format: <`value`><`qualifier`> where: `value` hours — Number of hours within the range 1 - 24. `qualifier` h — Indicates hours. NOTE:When a burst policy setting is applied initially or changed, the burst frequency interval begins and the storage that is associated with the policy will burst immediately, regardless of when the last burst occurred.
Effective IOPS limit	This is a read-only value that only applies to a shared policy. It is the total effective IOPS for all of the attached objects combined.
Effective KBPS limit	This is a read-only value that only applies to a shared policy. It is the total effective KBPS for all of the attached objects combined.