Configuring Fibre Channel Write Acceleration

This chapter describes the Fibre Channel Write Acceleration (FC-WA) feature, including how to enable the feature on Cisco NX-OS.

This chapter includes the following sections:

Information About Fibre Channel Write Acceleration

Fibre Channel Write Acceleration minimizes application latency or reduces transactions per second over long distances. For synchronous data replication, Fibre Channel Write Acceleration increases the distance of replication or reduces effective latency to improve performance. With this feature you can also configure the buffer count and change the number of 2-KB buffers reserved on the target side DPP for a SCSI flow.

To take advantage of this feature, both the initiator and target devices must be directly attached to an SSM.

The Fibre Channel Write Acceleration feature also allows the configuration of the buffer count. You can change the number of 2-KB buffers reserved on the target side DPP for a SCSI flow.

You can estimate the number of buffers to configure using the following formula:

(Number of concurrent SCSI writes * size of SCSI writes in bytes) / FCP data frame size in bytes

For example, HDS TrueCopy between HDS 9970s uses 1-KB FCP data frames. You perform an initial synchronization for a 16-LUN TrueCopy group with 15 tracks, or 768-KB per LUN, which requires approximately 16*(768*1024)/1024 or 12248 write buffers.

Note The Fibre Channel Write Acceleration feature requires the Enterprise Package license installed on both the initiator and target switches.

Note The initiator and target cannot connect to the same Cisco MDS switch. Fibre Channel Write Acceleration requires that the initiator and target must each connect to an SSM module installed on different Cisco MDS switches.

Note Fibre Channel Write Acceleration can only be provisioned on the entire SSM, not a group of interfaces on the SSM.

Licensing Requirements for Fibre Channel Write Acceleration

The following table shows the licensing requirements for Fibre Channel Write Acceleration:

 

License
License Description

ENTERPRISE_PKG

Fibre Channel Write Acceleration requires license. Any feature not included in a license package is bundled with the Cisco NX-OS system images and is provided at no extra charge to you. For a complete explanation of the NX-OS licensing scheme, see the Cisco NX-OS Licensing Guide .

Default Settings

Table 47-1 lists the default settings for Fibre Channel Write Acceleration parameters.

 

Table 47-1 Default Fibre Channel Write Acceleration Parameters

Parameters
Default

Fibre Channel Write Acceleration

Disabled

Fibre Channel Write Acceleration buffers

1024

Configuring Fibre Channel Write Acceleration

This section includes the following topics:

Enabling Fibre Channel Write Acceleration

To enable Fibre Channel Write Acceleration, and optionally modify the number of Write Acceleration buffers, follow these steps:

 

 
Command
Purpose

Step 1

config t

Example:

switch# config t

switch(config)#

Enters configuration mode.

Step 2

ssm enable feature scsi-flow module slot

Example:

switch(config)# ssm enable feature scsi-flow module 2

Enables SCSI flow services on the SSM in slot 2.

Note Fibre Channel Write Acceleration can only be configured on all interfaces on the SSM, not on groups of interfaces.

Step 3

scsi-flow flow-id flow-id initiator-vsan vsan-id initiator-pwwn wwn target-vsan vsan-id target-pwwn wwn

Example:

switch(config)# scsi-flow flow-id 3 initiator-vsan 2 initiator-pwwn 21:00:00:e0:8b:07:5f:aa target-vsan 4 target-pwwn 2a:20:00:05:30:00:77:e0

Configures SCSI flow identifier 3 using the pWWNs of the initiator and the target. The flow identifier range is 1 to 65535.

Step 4

scsi-flow distribute

Example:

switch(config)# scsi-flow distribute

Enables CFS distribution for the SCSI flow.

Note No CFS configuration commit operation is required for SCSI flow. The SCSI flow manager uses CFS for target validation.

Step 5

scsi-flow flow-id flow-id write-acceleration

Example:

switch(config)# scsi-flow flow-id 3 write-acceleration

Enables Fibre Channel Write Acceleration for SCSI flow identifier 3.

no scsi-flow flow-id 3 write-acceleration

Example:

switch(config)# no scsi-flow flow-id 3 write-acceleration

Disables SCSI flow Write Acceleration for SCSI flow identifier 3. The default is disabled.

Step 6

scsi-flow flow-id flow-id write-acceleration buffer count

Example:

switch(config)# scsi-flow flow-id 3 write-acceleration buffer 2048

Enables Fibre Channel Write Acceleration for SCSI flow identifier 3 and sets the number of buffers to 2048. The range is 1 to 40000.

no scsi-flow flow-id flow-id write-acceleration buffer count

Example:

switch(config)# no scsi-flow flow-id 3 write-acceleration buffer 1024

Reverts to the default number of Write Acceleration buffers. The default is 1024.

To enable Fibre Channel Write Acceleration, and optionally modify the number of Write Acceleration buffers using the DCNM-SAN, follow these steps:

Step 1 Expand End Devices and then select S SM Features from the Physical Attributes pane.

You see the Intelligent Storage Services configuration, showing the FCWA tab in the Information pane.

Step 2 Click Create Row in the Information pane to create a SCSI flow or click a row in the FCWA table to modify an existing SCSI flow.

You see the FC Write Acceleration dialog box.

Step 3 Select the initiator and target WWNs and VSAN IDs and check the WriteAcc check box to enable Fibre Channel Write Acceleration on this SCSI flow.

Step 4 (Optional) Enable SCSI flow statistics on this SCSI flow at this time by checking the Enable Statistics check box.

Step 5 (Optional) Set the BufCount value to the number of 2K buffers used by the SCSI target.

Step 6 Click Create to create this SCSI flow with Fibre Channel Write Acceleration.

Verifying Fibre Channel Write Acceleration

To display Fibre Channel Acceleration configuration information, perform one of the following tasks:

 

Command
Purpose

show scsi flow

Displays Fibre Channel Write Acceleration configuration for all SCSI flow identifiers.

show scsi-flow flow-id 3

Displays Fibre Channel Write Acceleration configuration for a specific SCSI flow identifiers.

For detailed information about the fields in the output from these commands, refer to the Cisco DC-OS Command Reference .

Displaying Fibre Channel Write Acceleration Information

Use the show scsi-flow command to display information about the status of the Fibre Channel Write Acceleration configuration (see Example 47-1 and Example 47-2).

Example 47-1 Displays Fibre Channel Write Acceleration Configuration for All SCSI Flow Identifiers

switch# show scsi-flow
Flow Id: 3
Initiator VSAN: 101
Initiator WWN: 21:00:00:e0:8b:05:76:28
Target VSAN: 102
Target WWN: 21:00:00:20:37:38:7f:7d
Target LUN: ALL LUNs
Flow Verification Status:
-------------------------
Initiator Verification Status: success
Target Verification Status: success
Initiator Linecard Status: success
Target Linecard Status: success
Feature Status:
---------------
Write-Acceleration enabled
Write-Acceleration Buffers: 1024
Configuration Status: success
Statistics enabled
Configuration Status: success
 
Flow Id: 4
Initiator VSAN: 101
Initiator WWN: 21:00:00:e0:8b:05:76:28
Target VSAN: 102
Target WWN: 21:00:00:20:37:38:a7:89
Target LUN: ALL LUNs
Flow Verification Status:
-------------------------
Initiator Verification Status: success
Target Verification Status: success
Initiator Linecard Status: success
Target Linecard Status: success
Feature Status:
---------------
Write-Acceleration enabled
Write-Acceleration Buffers: 1024
Configuration Status: success
Statistics enabled
Configuration Status: success
 

Example 47-2 Displays Fibre Channel Write Acceleration Configuration for a Specific SCSI Flow Identifier

switch# show scsi-flow flow-id 3
Flow Id: 3
Initiator VSAN: 101
Initiator WWN: 21:00:00:e0:8b:05:76:28
Target VSAN: 102
Target WWN: 21:00:00:20:37:38:7f:7d
Target LUN: ALL LUNs
Flow Verification Status:
-------------------------
Initiator Verification Status: success
Target Verification Status: success
Initiator Linecard Status: success
Target Linecard Status: success
Feature Status:
---------------
Write-Acceleration enabled
Write-Acceleration Buffers: 1024
Configuration Status: success
Statistics enabled
Configuration Status: success

Filed Description for Fibre Channel Write Acceleration

This section includes the following topics:

  • FCWA
  • SSM
  • Virtual Initiator
  • FCWA Config Status

FCWA

 

Field
Description

Flow Id

Represents the flow identifier.

Init WWN

Represents the pWWN of the initiator in the flow.

Init VSAN

The VSAN ID of the initiator on which the flow is configured.

Target WWN

Represents the pWWN of the target in the flow.

TargetVSAN

The VSAN ID of the target on which the flow is configured.

WriteAcc

Specifies if write-acceleration feature is enabled for this flow. If set to true it is enabled. If set to false, it is disabled.

BufCount

It specifies the number of buffers to be used for write-acceleration.

Stats Enable

Specifies if the statistics gathering needs to be enabled for this flow. If set to true, then it is enabled. If it is set to false, then it is disabled.

Stats Clear

Assists in clearing the statistics for this flow.

Init Verification

The verification status of the initiator device corresponding to the SCSI flow.

Init Module

The status of the linecard where the SCSI flow initiator device is located.

Target Verification

The verification status of the target device corresponding to the SCSI flow.

Target Module

The status of the linecard where the SCSI flow target device is located.

SSM

 

Field
Description

StartPort, EndPort, Feature

A table containing feature related information for interfaces. This table gives a list of interfaces that are assigned to different features. The interfaces supported are of the type Fibre Channel.

PartnerImageURI

A collection of objects related to SSM Feature to interface mapping.

Virtual Initiator

 

Field
Description

Processor Id

The DPP ID.

Control

If false, it’s the data path. If true, it’s the control path.

FCWA Config Status

 

Field
Description

Overall

The configuration status for write-acceleration feature for this flow.

Initiator

The initiator configuration status for write-acceleration feature for this flow.

Target

The target configuration status for write-acceleration feature for this flow.