Table Of Contents

Configuring Fibre Channel Write Acceleration

About Fibre Channel Write Acceleration

Enabling Fibre Channel Write Acceleration

Displaying SCSI Flow Services Information

Default Settings

Configuring Fibre Channel Write Acceleration

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The Storage Services Module (SSM) supports Intelligent Storage Services in Cisco MDS SAN-OS Release 2.0(2b) and later that include Fibre Channel write acceleration.

This chapter includes the following sections:

•About Fibre Channel Write Acceleration

•Enabling Fibre Channel Write Acceleration

•Displaying SCSI Flow Services Information

•Default Settings

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. 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, for HDS TrueCopy between HDS 9970s, which use 1KB FCP data frames, and you perform an initial sync for a 16-LUN TrueCopy group with 15 tracks, or 768 KB per LUN, the approximate number of write buffers required would be 16*(768*1024)/1024 or 12248 buffers.

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

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

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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	switch# config t switch(config)#	Enters configuration mode.
Step 2	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	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	switch(config)# scsi-flow flow-id 3 write-acceleration	Enables Fibre Channel write acceleration for SCSI flow identifier 3.
	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 5	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.
	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.

Displaying SCSI Flow Services Information

Use the show scsi-flow command to display information about the status of the Fibre Channel write acceleration configuration (see Example 39-1 and Example 39-2).

Example 39-1 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 39-2 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

Default Settings

Table 39-1 lists the default settings for Fibre Channel Write Acceleration parameters.

Table 39-1 Default Intelligent Storage Services Parameters 

Parameters	Default
Fibre Channel write acceleration	Disabled
Fibre Channel write acceleration buffers	1024