Fibre Channel (SAN)

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New Contributor
Posts: 3
Registered: ‎08-21-2013

Buffer Credits calculation help required.

Hi All,

Sorry for my intrusion ... I have a question regarding our FiberChannel configuration where I need Your help. We have two sites (main and DR) which are connected by two distinct ways via two Brocade DS200B and DS300B FB switches (via dark fiber). At present, the distance between the sites is 11km (roughly 7 miles) and everything works as expected without issue.

However in the coming months we will be relocating to a new DR site and the distance will be tripling (35km - 22miles). We will be using new GBICs to accomodate for the longer distance. The question at hand is: Do we need to change the buffer credits for those ports to accomodate or not and if yes, to what value. I am not a FC/network guy so couldn't calculate the expected/needed value by reading the user guide of the switched. At the moment the buffer credits are on value 8.

I'm sure a FC specialist has the right tool/info at hand and can easily answer this.

Thanks,

Pascal

Valued Contributor
Posts: 761
Registered: ‎06-11-2010

Re: Buffer Credits calculation help required.

Hi,

what is the current speed of the ISL?

and the current ISL configuration?

could you paste the output of portcfgshow <port>?

Depending on the current config, the buffers are automatically calculated and reserved or have to be configured manually.

rgds

New Contributor
Posts: 3
Registered: ‎08-21-2013

Re: Buffer Credits calculation help required.

Hi,

The current speed is 4GB and here is the requested output:

admin> portcfgshow 7

Area Number:              7

Speed Level:              AUTO

AL_PA Offset 13:          OFF

Trunk Port                ON

Long Distance             OFF

VC Link Init              OFF

Locked L_Port             OFF

Locked G_Port             ON

Disabled E_Port           OFF

ISL R_RDY Mode            OFF

RSCN Suppressed           OFF

Persistent Disable        OFF

NPIV capability           ON

QOS E_Port                OFF

In the webconsole I have additionally

Port Media lw

Port Type E-Port

Speed (GB/s) N4

F-Port BB Credit 8

Hope it says more to you than to me :-). Thanks

Valued Contributor
Posts: 761
Registered: ‎06-11-2010

Re: Buffer Credits calculation help required.

As per that output, the port does not have Long distance configured. If the distance is increased up to 35 Km you will need to activate this feature (which requires extended fabric license).

In order to configure configure the ISL, the command to use is portcfglongdistance. With this command you can modify the following settings of the port config:

Area Number:              7

Speed Level:              AUTO

AL_PA Offset 13:          OFF

Trunk Port                ON

Long Distance             OFF

VC Link Init              OFF

Locked L_Port             OFF

Locked G_Port             ON

Disabled E_Port           OFF

ISL R_RDY Mode            OFF

RSCN Suppressed           OFF

Persistent Disable        OFF

NPIV capability           ON

QOS E_Port                OFF

Usually depending on the xWDM equipment, you have to set VC LINK INIT and/or R_RDY. But, a standar Extended ISL config would be the one shown in the following example:

ED48K_133:root> portcfglongdistance 10/14

Usage: portCfgLongDistance PortNumber       Distance_Level <VC Translation Link Init> <Desired Distance for LD mode>

distance_level:         L0  : normal

                        LE  : <= 10km

                        LD  : auto

                        LS  : static

vc_trans_link_init:     0   normal

                        1   VC translation

desired_distance:       in Kilo-meters

                        valid for LD or LS level only

Please enter the long distance level -- LS

Please enter the vc translation link init -- 1

Please enter the desired distance (in Km) -- 35

Reserved Buffers =        76

ED48K_133:root>


As you can see, when you insert the distance, the switch automatically calculates the required number of BB credits (I recommend you to set the speed manually to 4G in this case). the only issue is that the switch calculates the number of required BB credits based on maximun size frames, and usually the average frame size through the ISL is smaller, so you could increase the desired distance in order to get more BB credits.



Rgds,

Felipon


New Contributor
Posts: 3
Registered: ‎08-21-2013

Re: Buffer Credits calculation help required.

Thanks Felipon. This is already very helpful ...

New Contributor
Posts: 2
Registered: ‎03-11-2010

Re: Buffer Credits calculation help required.

Hi Felipon,

What about "vc_translation_link_init" Does this need to be set and what does it do for an extended fabric?

Also, if I don't perform QoS zoning should I disable QoS on this port?  What does having it enabled vs disabled on that port if no QoS zoning is in tact?

SW6520_MDC_FAB_A:FID128:admin> portcfglongdistance 95 LS 1 -distance 25

Reserved Buffers =        206

Warning: port (95) may be reserving more credits depending on port speed.

SW6520_MDC_FAB_A:FID128:admin>

SW6520_MDC_FAB_A:FID128:admin> portcfgqos --enable 95

SW6520_MDC_FAB_A:FID128:admin>

SW6520_MDC_FAB_A:FID128:admin>

SW6520_MDC_FAB_A:FID128:admin> portcfgshow 95

Area Number: 95

Octet Speed Combo:        1(16G|8G|4G|2G)

Speed Level: AUTO(SW)

AL_PA Offset 13:          OFF

Trunk Port ON

Long Distance LS

VC Link Init ON

Desired Distance          25 Km

Reserved Buffers          220

Locked L_Port OFF

Locked G_Port ON

Disabled E_Port           OFF

Locked E_Port OFF

ISL R_RDY Mode            OFF

RSCN Suppressed           OFF

Persistent Disable        OFF

LOS TOV enable OFF

NPIV capability           ON

QOS Port ON

Port Auto Disable:        OFF

Rate Limit OFF

EX Port OFF

Mirror Port OFF

Credit Recovery           ON

F_Port Buffers            OFF

Fault Delay: 0(R_A_TOV)

NPIV PP Limit:            255

CSCTL mode: OFF

D-Port mode: OFF

D-Port over DWDM:         OFF

Compression: OFF

Encryption: OFF

FEC: ON


This is going directly over a "Dark Fiber" cable to another 6520 SAN Switch.


Matt

Valued Contributor
Posts: 761
Registered: ‎06-11-2010

Re: Buffer Credits calculation help required.

Hi Matt,

vc_translation_link_init sets the fillword used within the ISL. When '0' it uses IDLE primitives whilst when '1' it uses 'ARB'. Depending on the xWDM array, the speed of the link, you should use one or the other.


If QoS is not being used, keep it disabled. With long-distance ISLs there is not big difference, since there are no different VC assigned to the QoS zones.


Kind rgds,

Felipon

External Moderator
Posts: 4,787
Registered: ‎02-23-2004

Re: Buffer Credits calculation help required.

pascal,

"portbuffercalc" command help you to calculated required buffer credit.

or see this Article written by Dr. Steve Guendert

http://community.brocade.com/community/blogs/mainframe/blog/2013/02/27/buffer-credits-and-frame-size-calculation-in-fos-71

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