Configuring QoS
This section includes the following topics:
Information About Control Traffic
The Cisco MDS 9000 Family supports QoS for internally and externally generated control traffic. Within a switch, control traffic is sourced to the supervisor module and is treated as a high priority frame. A high priority status provides absolute priority over all other traffic and is assigned in the following cases:
-
Internally generated time-critical control traffic (mostly Class F frames).
-
Externally generated time-critical control traffic entering a switch in the Cisco MDS 9000 Family from a another vendor’s switch. High priority frames originating from other vendor switches are marked as high priority as they enter a switch in the Cisco MDS 9000 Family.
The Cisco MDS 9000 Family supports QoS for internally and externally generated control traffic. Within a switch, control traffic is sourced to the supervisor module and is treated as a high priority frame. A high priority status provides absolute priority over all other traffic and is assigned in the following cases:
-
Internally generated time-critical control traffic (mostly Class F frames).
-
Externally generated time-critical control traffic entering a switch in the Cisco MDS 9000 Family from a another vendor’s switch. High priority frames originating from other vendor switches are marked as high priority as they enter a switch in the Cisco MDS 9000 Family.
Enabling or Disabling Control Traffic
By default, the QoS feature for certain critical control traffic is enabled. These critical control frames are assigned the highest (absolute) priority.
Tip We do not recommend disabling this feature as all critical control traffic is automatically assigned the lowest priority once you issue this command.
To disable the high priority assignment for control traffic, follow these steps:
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|
|
Step 1
|
switch#
config t
|
Enters configuration mode.
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Step 2
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switch(config)#
no
qos control priority 0
|
Enables the control traffic QoS feature.
|
switch(config)#
qos control priority 0
|
Disables the control traffic QoS feature.
|
To enable or disable the high priority assignment for control traffic using Fabric Manager, follow these steps:
Step 1 Expand
Switches
, expand
FC Services
and then select
QoS
in the Physical Attributes pane.
The QoS control traffic information is displayed in the Information pane. The
Control
tab is default.
Step 2 Select the switch on which you want to enable or disable control traffic.
Step 3 In the Command column, click the drop-down menu and select
enable
or
disable
.
Step 4 Click
Apply Changes to save your changes
.
Displaying Control Traffic Information
Use the
show qos statistics
command to view the current state of the QoS configuration for critical control traffic. This command displays the current QoS settings along with the number of frames marked high priority. The count is only for debugging purposes and cannot be configured (see Example 57-1).
Example 57-1 Displays Current QoS Settings
switch# show qos statistics Total number of FC frames transmitted from the Supervisor= 15767 Number of highest-priority FC frames transmitted = 8224 Current priority of FC control frames = 0 (0 = lowest; 7 = highest)
Information About Data Traffic
Data traffic can be prioritized in distinct levels of service differentiation: low, medium, or high priority. You can apply QoS to ensure that Fibre Channel data traffic for your latency-sensitive applications receive higher priority over throughput-intensive applications such as data warehousing. With a deficit weighted round robin (DWRR) scheduler you can ensure that high priority traffic is treated better than low priority traffic. Online transaction processing (OLTP), which is a low volume, latency sensitive application, requires quick access to requested information. For example, DWRR weights of 70:20:10 implies that the high priority queue is serviced at 7 times the rate of the low priority queue. This guarantees lower delays and higher bandwidths to high priority traffic if congestion sets in. A similar configuration in the second switch ensures the same traffic treatment in the other direction.
Online transaction processing (OLTP), which is a low volume, latency sensitive application, requires quick access to requested information. Backup processing application require high bandwidth but are not sensitive to latency. In a network that does not support service differentiation, all traffic is treated identically—they experience similar latency and are allocated similar bandwidths. The QoS feature in the Cisco MDS 9000 Family switches provides these guarantees.
Data traffic can be prioritized in distinct levels of service differentiation: low, medium, or high priority. You can apply QoS to ensure that Fibre Channel data traffic for your latency-sensitive applications receive higher priority over throughput-intensive applications such as data warehousing (see Figure 57-1).
Figure 57-1 Prioritizing Data Traffic
In Figure 57-1, the OLTP traffic arriving at Switch 1 is marked with a high priority level of throughput classification (class map) and marking (policy map). Similarly, the backup traffic is marked with a low
priority level. The traffic is sent to the corresponding priority queue within a virtual output queue (VOQ).
A deficit weighted round robin (DWRR) scheduler configured in the first switch ensures that high priority traffic is treated better than low priority traffic. For example, DWRR weights of 70:20:10 implies that the high priority queue is serviced at 7 times the rate of the low priority queue. This guarantees lower delays and higher bandwidths to high priority traffic if congestion sets in. A similar configuration in the second switch ensures the same traffic treatment in the other direction.
If the ISL is congested when the OLTP server sends a request, the request is queued in the high priority queue and is serviced almost immediately since the high priority queue is not congested. The scheduler assigns its priority over the backup traffic in the low priority queue.
Note When the high priority queue does not have traffic flowing through, the low priority queue uses all the bandwidth and is not restricted to the configured value.
A similar occurrence in Switch 2 sends a response to the transaction request. The round trip delay experienced by the OLTP server is independent of the volume of low priority traffic or the ISL congestion. The backup traffic uses the available ISL bandwidth when it is not used by the OLTP traffic.
Comparing VSAN Versus Zone-Based QoS
While you can configure both zone-based QoS and VSAN-based QoS configurations in the same switch, both configurations have significant differences.
Table 57-1
highlights the differences between configuring QoS priorities based on VSANs versus zones.
Table 57-1 QoS Configuration Differences
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If you configure the active zone set on a given VSAN and also configure QoS parameters in any of the member zones, you cannot associate the policy map with the VSAN.
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You cannot activate a zone set on a VSAN that already has a policy map associated.
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If the same flow is present in two class maps associated to a policy map, the QoS value of the class map attached first takes effect.
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If the same flow is present in two zones in a given zone set with different QoS values, the higher QoS value is considered.
|
—
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During a zone merge, if the Cisco NX-OS software detects a mismatch for the QoS parameter, the link is isolated.
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Takes effect only when QoS is enabled.
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Takes effect only when QoS is enabled.
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Configuring Data Traffic
To configure QoS using Fabric Manager, follow these steps:
Step 1 Enable the QoS feature.
Step 2 Create and define class maps.
Step 3 Define service policies.
Step 4 Apply the configuration.
QoS Initiation for Data Traffic
By default, the QoS data traffic feature is disabled for data traffic. To configure QoS for data traffic, you must first enable the data traffic feature in the switch.
Tip QoS is supported in interoperability mode. For more information, refer to the Cisco MDS 9000 Family Switch-to-Switch Interoperability Configuration Guide.
To enable the QoS data traffic feature, follow these steps:
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Step 1
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switch#
config t
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Enters configuration mode.
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Step 2
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switch(config)#
qos enable
|
Enables QoS. You can now configure data traffic parameters.
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switch(config)#
no qos enable
|
Removes the currently applied QoS configuration and disables QoS. You can no longer configure data traffic parameters.
|
Information About Class Map Creation
Using the class map feature you can create and define traffic class with match criteria to identify traffic belonging to that class. The class map name is restricted to 63 alphanumeric characters and defaults to the match-all option. Flow-based traffic uses one of the following values:
-
WWN—The source WWN or the destination WWN.
-
Fibre Channel ID (FC ID) —The source ID (SID) or the destination ID (DID).
-
Source interface—The ingress interface.
Use the class map feature to create and define a traffic class with match criteria to identify traffic belonging to that class. The class map name is restricted to 63 alphanumeric characters and defaults to the match-all option. Flow-based traffic uses one of the following values:
-
WWN—The source WWN or the destination WWN.
-
Fibre Channel ID (FC ID) —The source ID (SID) or the destination ID (DID). The possible values for mask are FFFFFF (the entire FC ID is used—this is the default), FFFF00 (only domain and area FC ID is used), or FF0000 (only domain FC ID is used).
Note An SID or DID of 0x000000 is not allowed.
-
Source interface—The ingress interface.
Tip The order of entries to be matched within a class map is not significant.
Creating a Class Map
Use the
class-map
command to create and define a traffic class with match criteria to identify traffic belonging to that class. Define each match criterion with one match statement from the class map configuration (switch(config-cmap)) mode.
-
Use the
source-wwn
option to specify the source WWN or the
destination-wwn
option to specify the destination WWN.
-
Use the
source-address
option to specify the source ID (SID) or the
destination-address
option to specify the destination ID (DID).
-
Use the
input-interface
option to specify the ingress interface.
-
Use the
destination-device-alias
option to specify the distributed device alias.
To create a class map, follow these steps:
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Step 1
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switch(config)#
qos class-map MyClass match-all
switch(config-cmap)#
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Specifies a logical AND operator for all matching statements in this class. If a frame matches all (default) configured criteria, it qualifies for this class. This is the default.
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switch(config)#
qos class-map MyClass match-any
switch(config-cmap)#
|
Specifies a logical OR operator for all matching statements in this class. If a frame matches any one configured criteria, it qualifies for this class.
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Step 2
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switch(config-cmap)#
match destination-address 0x12ee00
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Specifies a destination address match for frames with the specified destination FC ID.
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switch(config-cmap)#
match source-address 0x6d1090 mask 0xFFFFFF
|
Specifies a source address and mask match for frames with the specified source FC ID.
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switch(config-cmap)#
match destination-wwn 20:01:00:05:30:00:28:df
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Specifies a destination WWN to match frames.
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switch(config-cmap)#
match source-wwn 23:15:00:05:30:00:2a:1f
|
Specifies a source WWN to match frames.
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switch(config-cmap)#
match destination-device-alias DocDeviceAlias
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Specifies a destination device alias to match frames.
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switch(config-cmap)#
match source-device-alias DocDeviceAliase
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Specifies a source device alias to match frames.
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switch(config-cmap)#
match input-interface fc 2/1
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Specifies a source interface to match frames.
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switch(config-cmap)#
no
match input-interface fc 3/5
|
Removes a match based on the specified source interface.
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To create a class map using Fabric Manager, follow these steps:
Step 1 Expand
Switches
, expand
FC Services
and then select
QoS
in the Physical Attributes pane.
The QoS information is displayed in the Information pane. The
Control
tab is the default.
Step 2 In the
Class Maps
tab, click
Create Row
to create a new class map.
You see the Create Class Maps dialog box.
Step 3 Select the switches for the class map.
Step 4 Enter the source ID or the destination
ID
in the field.
Step 5 Enter a name for the class map.
Step 6 Select a Match mode.You can either match
any
or
all
criterion with one match statement from the class map configuration mode.
Step 7 Click
Create
to proceed with creating the class map.
Information About Service Policy Definition
Service policies are specified using policy maps. Policy maps provide an ordered mapping of class maps to service levels. The order of the class maps within a policy map is important to determine the order in which the frame is compared to class maps. The first matching class map has the corresponding priority marked in the frame. You can specify multiple class maps within a policy map, and map a class map to a high, medium, or low service level. The default priority is low. Alternatively, you can map a class map to a differentiated services code point (DSCP). The DSCP is an indicator of the service level for a specified frame.
Service policies are specified using policy maps. Policy maps provide an ordered mapping of class maps to service levels. You can specify multiple class maps within a policy map, and map a class map to a high, medium, or low service level. The default priority is low. The policy map name is restricted to 63 alphanumeric characters.
As an alternative, you can map a class map to a differentiated services code point (DSCP).The DSCP is an indicator of the service level for a specified frame. The DSCP value ranges from 0 to 63, and the default is 0. A DSCP value of 46 is disallowed.
The order of the class maps within a policy map is important to determine the order in which the frame is compared to class maps. The first matching class map has the corresponding priority marked in the frame.
Note Refer to http://www.cisco.com/en/US/tech/tk543/tk757/technologies_tech_note09186a00800949f2.shtml for further information on implementing QoS DSCP values.
Note Class maps are processed in the order in which they are configured in each policy map.
Specifying Service Policies
To specify a service policy, follow these steps:
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Step 1
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switch(config)#
qos policy-map MyPolicy
switch(config-pmap)#
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Creates a policy map called MyPolicy and places you in the policy-map submode.
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switch(config)#
no
qos policy-map OldPolicy
switch(config)#
|
Deletes the policy map called OldPolicy and places you in the policy-map submode.
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Step 2
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switch(config-pmap)#
class MyClass
switch(config-pmap-c)#
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Specifies the name of a predefined class and places you at the policy-map submode for that class.
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switch(config-pmap)#
no
class OldClass
|
Removes the class map called OldClass from the policy map.
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Step 3
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switch(config-pmap-c)#
priority high
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Specifies the priority to be given for each frame matching this class.
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switch(config-pmap-c)#
no priority high
|
Deletes a previously assigned priority and reverts to the default value of low.
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Step 4
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switch(config-pmap-c)#
dscp 2
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Specifies the DSCP value to mark each frame matching this class.
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switch(config-pmap-c)#
no dscp 60
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Deletes a previously assigned DSCP value and reverts to the factory default of 0.
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About Service Policy Enforcement
When you have configured a QoS data traffic policy, you must enforce the data traffic configuration by applying that policy to the required VSAN(s). If you do not apply the policy to a VSAN, the data traffic configuration is not enforced. You can only apply one policy map to a VSAN.
Note You can apply the same policy to a range of VSANs.
Applying Service Policies
To apply a service policy, follow these steps:
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Step 1
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switch(config)#
qos service policy MyPolicy vsan 3
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Applies a configured policy to VSAN 3.
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switch(config)#
no
qos service policy OldPolicy vsan 7
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Deletes a configured policy that was applied to VSAN 7.
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About the DWRR Traffic Scheduler Queue
The DWRR scheduler services the queues in the ratio of the configured weights. Higher weights translate to proportionally higher bandwidth and lower latency. The default weights are 50 for the high queue, 30 for the medium queue, and 20 for the low queue. The Cisco NX-OS software supports four scheduling queues:
-
Strict priority queues are queues that are serviced in preference to other queues—it is always serviced if there is a frame queued in it regardless of the state of the other queues.
-
QoS assigns all other traffic to the DWRR scheduling high, medium, and low priority traffic queues.
The Cisco NX-OS software supports four scheduling queues:
-
Strict priority queues are queues that are serviced in preference to other queues—it is always serviced if there is a frame queued in it regardless of the state of the other queues.
-
QoS assigns all other traffic to the DWRR scheduling high, medium, and low priority traffic queues.
The DWRR scheduler services the queues in the ratio of the configured weights. Higher weights translate to proportionally higher bandwidth and lower latency. The default weights are 50 for the high queue, 30 for the medium queue, and 20 for the low queue. Decreasing order of queue weights is mandated to ensure the higher priority queues have a higher service level, though the ratio of the configured weights can vary (for example, one can configure 70:30:5 or 60:50:10 but not 50:70:10).
Table 57-2
describes the QoS behavior for Generation 1, Generation 2, and Generation 3 switching modules.
Table 57-2 QoS Behavior for Generation 1 and Generation 2 Switching Modules
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Generation 1
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Generation 1
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QoS behavior reflects the DWRR configuration for traffic coming in through a given port and queued to the same egress port. All the other traffic share equal bandwidth.
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Generation 1
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Generation 2 or Generation 3
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QoS behavior reflects the DWRR configuration for traffic coming in through a given port and queued to the same egress port. All the other streams share equal bandwidth.
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Generation 2 or Generation 3
|
Generation 1
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Bandwidth partitioning is equal for all the traffic.
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Generation 2 or Generation 3
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Generation 2 or Generation 3
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QoS behavior reflects the DWRR weights configuration for all possible streams.
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Changing the Weight in a DWRR Queue
To associate a weight with a DWRR queue, follow these steps:
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Step 1
|
switch(config)#
qos dwrr-q high weight 10
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Associates a relative weight (10) to a specified queue (default queue).
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switch(config)#
no
qos dwrr-q low weight 51
|
Restores the default weight of 20.
|
To change the weight in a DWRR queue using Fabric Manager, follow these steps:
Step 1 Expand
Switches
, expand
FC Services
and then select
QoS
in the Physical Attributes pane.
The QoS control traffic information is displayed in the Information pane. The default is the
Control
tab.
Step 2 Click the
DWRR
tab.
You see the queue status and weight.
Step 3 Select a switch and change the weight.
Step 4 Click the
Apply Changes icon to save your changes
.
Displaying Data Traffic Information
Examples
The
show qos
commands display the current QoS settings for data traffic (see Examples
57-2
to
57-10
).
Example 57-2 Displays the Contents of all Class Maps
switch# show qos class-map qos class-map MyClass match-any match destination-wwn 20:01:00:05:30:00:28:df match source-wwn 23:15:00:05:30:00:2a:1f match input-interface fc2/1 qos class-map Class2 match-all match input-interface fc2/14 qos class-map Class3 match-all match source-wwn 20:01:00:05:30:00:2a:1f
Example 57-3 Displays the Contents of a Specified Class Map
switch# show qos class-map name MyClass qos class-map MyClass match-any match destination-wwn 20:01:00:05:30:00:28:df match source-wwn 23:15:00:05:30:00:2a:1f match input-interface fc2/1
Example 57-4 Displays All Configured Policy Maps
switch# show qos policy-map
Example 57-5 Displays a Specified Policy Map
switch# show qos policy-map name MyPolicy
Example 57-6 Displays Scheduled DWRR Configurations
qos dwrr-q high weight 50 qos dwrr-q medium weight 30
Example 57-7 Displays All Applied Policy Maps
switch# show qos service policy qos service policy MyPolicy vsan 1 qos service policy Policy1 vsan 4
Example 57-8 Displays the Policy Map Associated with a Specified VSAN
switch# show qos service policy vsan 1
Example 57-9 Displays the Class Map Associated with a Specified Interface
switch# show qos service policy interface fc3/10
Example 57-10 Displays QoS Statistics
switch# show qos statistics Total number of FC frames transmitted from the Supervisor= 301431 Number of highest-priority FC frames transmitted = 137679 Current priority of FC control frames = 7 (0 = lowest; 7 = highest)
Configuration Examples for QoS
This section describes a configuration example for the application illustrated in Figure 57-2.
Figure 57-2 Example Application for Traffic Prioritization
Both the OLTP server and the backup server are accessing the disk. The backup server is writing large amounts of data to the disk. This data does not require specific service guarantees. The volumes of data generated by the OLTP server to the disk are comparatively much lower but this traffic requires faster response because transaction processing is a low latency application.
The point of congestion is the link between Switch 2 and the disk, for traffic from the switch to the disk. The return path is largely uncongested as there is little backup traffic on this path.
Service differentiation is needed at Switch 2 to prioritize the OLTP-server-to-disk traffic higher than the backup-server-to-disk traffic.
To configure traffic prioritization for the example application, follow these steps:
Step 1 Create the class maps.
Switch 2(config)# qos class-map jc1 match-all Switch 2(config-cmap)# match source-wwn 21:00:00:0c:50:02:ca:b5 Switch 2(config-cmap)# match destination-wwn 22:00:00:04:cf:22:eb:dc Switch 2(config-cmap)# exit Switch 2(config)# qos class-map jc2 match-all Switch 2(config-cmap)# match source-wwn 21:00:00:0c:50:02:c7:ff Switch 2(config-cmap)# match destination-wwn 22:00:00:04:cf:22:eb:dc Switch 2(config-cmap)# exit
Step 2 Create the policy map.
Switch 2(config)# qos policy-map jp1 Switch 2(config-pmap)# class jc1 Switch 2(config-pmap-c)# priority high Switch 2(config-pmap-c)# exit Switch 2(config-pmap)# class jc2 Switch 2(config-pmap-c)# priority low Switch 2(config-pmap-c)# exit Switch 2(config-pmap)# exit
Step 3 Assign the service policy.
Switch 2(config)# qos service policy jp1 vsan 1
Step 4 Assign the weights for the DWRR queues.
Switch 2(config)# qos dwrr-q high weight 50 Switch 2(config)# qos dwrr-q medium weight 30 Switch 2(config)# qos dwrr-q low weight 20
Step 5 Repeat Create the class maps. through Assign the weights for the DWRR queues. on Switch 1 to address forward path congestion at both switches.
Congestion could occur anywhere in the example configuration. To address congestion of the return path at both switches, you need to create two more class maps and include them in the policy map as follows:
Step 1 Create two more class maps.
Switch 2(config)# qos class-map jc3 match-all Switch 2(config-cmap)# match source-wwn 22:00:00:04:cf:22:eb:dc Switch 2(config-cmap)# match destination-wwn 21:00:00:0c:50:02:ca:b5 Switch 2(config-cmap)# exit Switch 2(config)# qos class-map jc4 match-all Switch 2(config-cmap)# match source-wwn 22:00:00:04:cf:22:eb:dc Switch 2(config-cmap)# match destination-wwn 21:00:00:0c:50:02:c7:ff Switch 2(config-cmap)# exit
Step 2 Assign the class maps to the policy map.
Switch 2(config)# qos policy-map jp1 Switch 2(config-pmap)# class jc3 Switch 2(config-pmap-c)# priority high Switch 2(config-pmap-c)# exit Switch 2(config-pmap)# class jc4 Switch 2(config-pmap-c)# priority low Switch 2(config-pmap-c)# exit Switch 2(config-pmap)# exit
Step 3 Repeat Create two more class maps. through Assign the class maps to the policy map. on Switch 1 to address return path congestion at both switches.