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. |
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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 1 lists the default settings for 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 using the DCNM-SAN, follow these steps:
Procedure
Step 1 |
Expand End Devices and then select SSM 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. |
Filed Description for Fibre Channel Write Acceleration
This section includes the following topics:
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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. |